diff --git a/integration/simple-long/google/protobuf/wrappers.bin b/integration/simple-long/google/protobuf/wrappers.bin
index ba0182a94..136184cf8 100644
Binary files a/integration/simple-long/google/protobuf/wrappers.bin and b/integration/simple-long/google/protobuf/wrappers.bin differ
diff --git a/integration/simple-long/google/protobuf/wrappers.ts b/integration/simple-long/google/protobuf/wrappers.ts
index 3605ad6ae..26ad3cd97 100644
--- a/integration/simple-long/google/protobuf/wrappers.ts
+++ b/integration/simple-long/google/protobuf/wrappers.ts
@@ -230,11 +230,7 @@ export const Int64Value = {
 
   fromPartial(object: DeepPartial<Int64Value>): Int64Value {
     const message = { ...baseInt64Value } as Int64Value;
-    if (object.value !== undefined && object.value !== null) {
-      message.value = object.value as Long;
-    } else {
-      message.value = Long.ZERO;
-    }
+    message.value = object.value !== undefined && object.value !== null ? Long.fromValue(object.value) : Long.ZERO;
     return message;
   },
 };
@@ -281,11 +277,7 @@ export const UInt64Value = {
 
   fromPartial(object: DeepPartial<UInt64Value>): UInt64Value {
     const message = { ...baseUInt64Value } as UInt64Value;
-    if (object.value !== undefined && object.value !== null) {
-      message.value = object.value as Long;
-    } else {
-      message.value = Long.UZERO;
-    }
+    message.value = object.value !== undefined && object.value !== null ? Long.fromValue(object.value) : Long.UZERO;
     return message;
   },
 };
@@ -560,9 +552,11 @@ function base64FromBytes(arr: Uint8Array): string {
   return btoa(bin.join(''));
 }
 
-type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined | Long;
+type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
 export type DeepPartial<T> = T extends Builtin
   ? T
+  : T extends Long
+  ? string | number | Long
   : T extends Array<infer U>
   ? Array<DeepPartial<U>>
   : T extends ReadonlyArray<infer U>
diff --git a/integration/simple-long/simple-test.ts b/integration/simple-long/simple-test.ts
new file mode 100644
index 000000000..79f942076
--- /dev/null
+++ b/integration/simple-long/simple-test.ts
@@ -0,0 +1,76 @@
+import { SimpleWithMap } from './simple';
+
+describe('simple', () => {
+  it('can fromPartial maps', () => {
+    const s1 = SimpleWithMap.fromPartial({
+      intLookup: { 1: 2, 2: 1 },
+      longLookup: { '1': 2, '2': 1 },
+    });
+    expect(s1).toMatchInlineSnapshot(`
+      Object {
+        "intLookup": Object {
+          "1": 2,
+          "2": 1,
+        },
+        "longLookup": Object {
+          "1": Long {
+            "high": 0,
+            "low": 2,
+            "unsigned": false,
+          },
+          "2": Long {
+            "high": 0,
+            "low": 1,
+            "unsigned": false,
+          },
+        },
+        "nameLookup": Object {},
+      }
+    `);
+  });
+
+  it('can toJSON/fromJSON maps', () => {
+    const s1 = SimpleWithMap.fromPartial({
+      intLookup: { 1: 2, 2: 1 },
+      longLookup: { '1': 2, '2': 1 },
+    });
+
+    const json = SimpleWithMap.toJSON(s1);
+    expect(json).toMatchInlineSnapshot(`
+      Object {
+        "intLookup": Object {
+          "1": 2,
+          "2": 1,
+        },
+        "longLookup": Object {
+          "1": "2",
+          "2": "1",
+        },
+        "nameLookup": Object {},
+      }
+    `);
+
+    const s2 = SimpleWithMap.fromJSON(JSON.parse(JSON.stringify(json)));
+    expect(s2).toMatchInlineSnapshot(`
+      Object {
+        "intLookup": Object {
+          "1": 2,
+          "2": 1,
+        },
+        "longLookup": Object {
+          "1": Long {
+            "high": 0,
+            "low": 2,
+            "unsigned": false,
+          },
+          "2": Long {
+            "high": 0,
+            "low": 1,
+            "unsigned": false,
+          },
+        },
+        "nameLookup": Object {},
+      }
+    `);
+  });
+});
diff --git a/integration/simple-long/simple.bin b/integration/simple-long/simple.bin
index 427793dea..b1ad8ee48 100644
Binary files a/integration/simple-long/simple.bin and b/integration/simple-long/simple.bin differ
diff --git a/integration/simple-long/simple.proto b/integration/simple-long/simple.proto
index c7bbc8419..9c812fc70 100644
--- a/integration/simple-long/simple.proto
+++ b/integration/simple-long/simple.proto
@@ -14,6 +14,8 @@ message SimpleWithWrappers {
 message SimpleWithMap {
   map<string, string> nameLookup = 2;
   map<int32, int32> intLookup = 3;
+  // Ideally we'd test map<int64, int64> but we present maps as JS objects and `Long` cannot be used as a keys.
+  map<string, int64> longLookup = 4;
 }
 
 message Numbers {
diff --git a/integration/simple-long/simple.ts b/integration/simple-long/simple.ts
index bc06e402b..55dfae0da 100644
--- a/integration/simple-long/simple.ts
+++ b/integration/simple-long/simple.ts
@@ -17,6 +17,8 @@ export interface SimpleWithWrappers {
 export interface SimpleWithMap {
   nameLookup: { [key: string]: string };
   intLookup: { [key: number]: number };
+  /** Ideally we'd test map<int64, int64> but we present maps as JS objects and `Long` cannot be used as a keys. */
+  longLookup: { [key: string]: Long };
 }
 
 export interface SimpleWithMap_NameLookupEntry {
@@ -29,6 +31,11 @@ export interface SimpleWithMap_IntLookupEntry {
   value: number;
 }
 
+export interface SimpleWithMap_LongLookupEntry {
+  key: string;
+  value: Long;
+}
+
 export interface Numbers {
   double: number;
   float: number;
@@ -142,11 +149,8 @@ export const SimpleWithWrappers = {
     message.name = object.name ?? undefined;
     message.age = object.age ?? undefined;
     message.enabled = object.enabled ?? undefined;
-    if (object.bananas !== undefined && object.bananas !== null) {
-      message.bananas = object.bananas as Long | undefined;
-    } else {
-      message.bananas = undefined;
-    }
+    message.bananas =
+      object.bananas !== undefined && object.bananas !== null ? Long.fromValue(object.bananas) : undefined;
     message.coins = (object.coins ?? []).map((e) => e);
     message.snacks = (object.snacks ?? []).map((e) => e);
     return message;
@@ -163,6 +167,9 @@ export const SimpleWithMap = {
     Object.entries(message.intLookup).forEach(([key, value]) => {
       SimpleWithMap_IntLookupEntry.encode({ key: key as any, value }, writer.uint32(26).fork()).ldelim();
     });
+    Object.entries(message.longLookup).forEach(([key, value]) => {
+      SimpleWithMap_LongLookupEntry.encode({ key: key as any, value }, writer.uint32(34).fork()).ldelim();
+    });
     return writer;
   },
 
@@ -172,6 +179,7 @@ export const SimpleWithMap = {
     const message = { ...baseSimpleWithMap } as SimpleWithMap;
     message.nameLookup = {};
     message.intLookup = {};
+    message.longLookup = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -187,6 +195,12 @@ export const SimpleWithMap = {
             message.intLookup[entry3.key] = entry3.value;
           }
           break;
+        case 4:
+          const entry4 = SimpleWithMap_LongLookupEntry.decode(reader, reader.uint32());
+          if (entry4.value !== undefined) {
+            message.longLookup[entry4.key] = entry4.value;
+          }
+          break;
         default:
           reader.skipType(tag & 7);
           break;
@@ -209,6 +223,12 @@ export const SimpleWithMap = {
         message.intLookup[Number(key)] = Number(value);
       });
     }
+    message.longLookup = {};
+    if (object.longLookup !== undefined && object.longLookup !== null) {
+      Object.entries(object.longLookup).forEach(([key, value]) => {
+        message.longLookup[key] = Long.fromString(value as string);
+      });
+    }
     return message;
   },
 
@@ -226,6 +246,12 @@ export const SimpleWithMap = {
         obj.intLookup[k] = v;
       });
     }
+    obj.longLookup = {};
+    if (message.longLookup) {
+      Object.entries(message.longLookup).forEach(([k, v]) => {
+        obj.longLookup[k] = v.toString();
+      });
+    }
     return obj;
   },
 
@@ -247,6 +273,14 @@ export const SimpleWithMap = {
         }
       });
     }
+    message.longLookup = {};
+    if (object.longLookup !== undefined && object.longLookup !== null) {
+      Object.entries(object.longLookup).forEach(([key, value]) => {
+        if (value !== undefined) {
+          message.longLookup[key] = Long.fromValue(value);
+        }
+      });
+    }
     return message;
   },
 };
@@ -363,6 +397,62 @@ export const SimpleWithMap_IntLookupEntry = {
   },
 };
 
+const baseSimpleWithMap_LongLookupEntry: object = { key: '', value: Long.ZERO };
+
+export const SimpleWithMap_LongLookupEntry = {
+  encode(message: SimpleWithMap_LongLookupEntry, writer: Writer = Writer.create()): Writer {
+    if (message.key !== '') {
+      writer.uint32(10).string(message.key);
+    }
+    if (!message.value.isZero()) {
+      writer.uint32(16).int64(message.value);
+    }
+    return writer;
+  },
+
+  decode(input: Reader | Uint8Array, length?: number): SimpleWithMap_LongLookupEntry {
+    const reader = input instanceof Reader ? input : new Reader(input);
+    let end = length === undefined ? reader.len : reader.pos + length;
+    const message = { ...baseSimpleWithMap_LongLookupEntry } as SimpleWithMap_LongLookupEntry;
+    while (reader.pos < end) {
+      const tag = reader.uint32();
+      switch (tag >>> 3) {
+        case 1:
+          message.key = reader.string();
+          break;
+        case 2:
+          message.value = reader.int64() as Long;
+          break;
+        default:
+          reader.skipType(tag & 7);
+          break;
+      }
+    }
+    return message;
+  },
+
+  fromJSON(object: any): SimpleWithMap_LongLookupEntry {
+    const message = { ...baseSimpleWithMap_LongLookupEntry } as SimpleWithMap_LongLookupEntry;
+    message.key = object.key !== undefined && object.key !== null ? String(object.key) : '';
+    message.value = object.value !== undefined && object.value !== null ? Long.fromString(object.value) : Long.ZERO;
+    return message;
+  },
+
+  toJSON(message: SimpleWithMap_LongLookupEntry): unknown {
+    const obj: any = {};
+    message.key !== undefined && (obj.key = message.key);
+    message.value !== undefined && (obj.value = (message.value || Long.ZERO).toString());
+    return obj;
+  },
+
+  fromPartial(object: DeepPartial<SimpleWithMap_LongLookupEntry>): SimpleWithMap_LongLookupEntry {
+    const message = { ...baseSimpleWithMap_LongLookupEntry } as SimpleWithMap_LongLookupEntry;
+    message.key = object.key ?? '';
+    message.value = object.value !== undefined && object.value !== null ? Long.fromValue(object.value) : Long.ZERO;
+    return message;
+  },
+};
+
 const baseNumbers: object = {
   double: 0,
   float: 0,
@@ -535,43 +625,27 @@ export const Numbers = {
     message.double = object.double ?? 0;
     message.float = object.float ?? 0;
     message.int32 = object.int32 ?? 0;
-    if (object.int64 !== undefined && object.int64 !== null) {
-      message.int64 = object.int64 as Long;
-    } else {
-      message.int64 = Long.ZERO;
-    }
+    message.int64 = object.int64 !== undefined && object.int64 !== null ? Long.fromValue(object.int64) : Long.ZERO;
     message.uint32 = object.uint32 ?? 0;
-    if (object.uint64 !== undefined && object.uint64 !== null) {
-      message.uint64 = object.uint64 as Long;
-    } else {
-      message.uint64 = Long.UZERO;
-    }
+    message.uint64 = object.uint64 !== undefined && object.uint64 !== null ? Long.fromValue(object.uint64) : Long.UZERO;
     message.sint32 = object.sint32 ?? 0;
-    if (object.sint64 !== undefined && object.sint64 !== null) {
-      message.sint64 = object.sint64 as Long;
-    } else {
-      message.sint64 = Long.ZERO;
-    }
+    message.sint64 = object.sint64 !== undefined && object.sint64 !== null ? Long.fromValue(object.sint64) : Long.ZERO;
     message.fixed32 = object.fixed32 ?? 0;
-    if (object.fixed64 !== undefined && object.fixed64 !== null) {
-      message.fixed64 = object.fixed64 as Long;
-    } else {
-      message.fixed64 = Long.UZERO;
-    }
+    message.fixed64 =
+      object.fixed64 !== undefined && object.fixed64 !== null ? Long.fromValue(object.fixed64) : Long.UZERO;
     message.sfixed32 = object.sfixed32 ?? 0;
-    if (object.sfixed64 !== undefined && object.sfixed64 !== null) {
-      message.sfixed64 = object.sfixed64 as Long;
-    } else {
-      message.sfixed64 = Long.ZERO;
-    }
-    message.manyUint64 = (object.manyUint64 ?? []).map((e) => e);
+    message.sfixed64 =
+      object.sfixed64 !== undefined && object.sfixed64 !== null ? Long.fromValue(object.sfixed64) : Long.ZERO;
+    message.manyUint64 = (object.manyUint64 ?? []).map((e) => Long.fromValue(e));
     return message;
   },
 };
 
-type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined | Long;
+type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
 export type DeepPartial<T> = T extends Builtin
   ? T
+  : T extends Long
+  ? string | number | Long
   : T extends Array<infer U>
   ? Array<DeepPartial<U>>
   : T extends ReadonlyArray<infer U>
diff --git a/integration/simple/simple-json-test.ts b/integration/simple/simple-json-test.ts
index 7891a5f5d..cf3d6059f 100644
--- a/integration/simple/simple-json-test.ts
+++ b/integration/simple/simple-json-test.ts
@@ -190,6 +190,7 @@ describe('simple json', () => {
         "intLookup": Object {
           "1": 0,
         },
+        "longLookup": Object {},
         "mapOfBytes": Object {},
         "mapOfStringValues": Object {},
         "mapOfTimestamps": Object {},
@@ -212,6 +213,7 @@ describe('simple json', () => {
       Object {
         "entitiesById": Object {},
         "intLookup": Object {},
+        "longLookup": Object {},
         "mapOfBytes": Object {},
         "mapOfStringValues": Object {},
         "mapOfTimestamps": Object {
@@ -236,12 +238,14 @@ describe('simple json', () => {
         b: new Uint8Array([1, 2, 3]),
       },
       mapOfStringValues: {},
+      longLookup: {},
     };
     const json = SimpleWithMap.toJSON(s1);
     expect(json).toMatchInlineSnapshot(`
       Object {
         "entitiesById": Object {},
         "intLookup": Object {},
+        "longLookup": Object {},
         "mapOfBytes": Object {
           "a": "AQI=",
           "b": "AQID",
@@ -265,6 +269,7 @@ describe('simple json', () => {
       Object {
         "entitiesById": Object {},
         "intLookup": Object {},
+        "longLookup": Object {},
         "mapOfBytes": Object {
           "a": Uint8Array [
             1,
diff --git a/integration/simple/simple-test.ts b/integration/simple/simple-test.ts
index f6d6c79a9..f87be3048 100644
--- a/integration/simple/simple-test.ts
+++ b/integration/simple/simple-test.ts
@@ -232,8 +232,10 @@ describe('simple', () => {
       mapOfTimestamps: {},
       mapOfBytes: {},
       mapOfStringValues: { a: '1', b: '', c: undefined },
+      longLookup: { 1: 2, 2: 1 },
     };
-    const s2 = PbSimpleWithMap.toObject(PbSimpleWithMap.decode(SimpleWithMap.encode(s1).finish()));
+    // const s2 = PbSimpleWithMap.toObject(PbSimpleWithMap.decode(SimpleWithMap.encode(s1).finish()));
+    const s2 = SimpleWithMap.decode(SimpleWithMap.encode(s1).finish());
     expect(s2).toMatchInlineSnapshot(`
       Object {
         "entitiesById": Object {
@@ -248,12 +250,16 @@ describe('simple', () => {
           "1": 2,
           "2": 1,
         },
+        "longLookup": Object {
+          "1": 2,
+          "2": 1,
+        },
+        "mapOfBytes": Object {},
         "mapOfStringValues": Object {
-          "a": Object {
-            "value": "1",
-          },
-          "b": Object {},
+          "a": "1",
+          "b": "",
         },
+        "mapOfTimestamps": Object {},
         "nameLookup": Object {
           "foo": "bar",
         },
@@ -269,6 +275,7 @@ describe('simple', () => {
       mapOfTimestamps: {},
       mapOfBytes: {},
       mapOfStringValues: { foo: '', bar: undefined },
+      longLookup: { 1: 2, 2: 1 },
     };
     const s2 = SimpleWithMap.decode(SimpleWithMap.encode(s1).finish());
     expect(s2).toEqual(s1);
@@ -317,6 +324,7 @@ describe('simple', () => {
     const s1 = SimpleWithMap.fromPartial({
       intLookup: { 1: 2, 2: 0 },
       mapOfStringValues: { a: '1', b: '', c: undefined },
+      longLookup: { 1: 2, 2: 0 },
     });
     expect(s1).toMatchInlineSnapshot(`
       Object {
@@ -325,6 +333,10 @@ describe('simple', () => {
           "1": 2,
           "2": 0,
         },
+        "longLookup": Object {
+          "1": 2,
+          "2": 0,
+        },
         "mapOfBytes": Object {},
         "mapOfStringValues": Object {
           "a": "1",
diff --git a/integration/simple/simple.bin b/integration/simple/simple.bin
index 8ebaa258b..eb98fb18e 100644
Binary files a/integration/simple/simple.bin and b/integration/simple/simple.bin differ
diff --git a/integration/simple/simple.proto b/integration/simple/simple.proto
index a7c6dad79..98ad06038 100644
--- a/integration/simple/simple.proto
+++ b/integration/simple/simple.proto
@@ -97,6 +97,7 @@ message SimpleWithMap {
   map<string, google.protobuf.Timestamp> mapOfTimestamps = 4;
   map<string, bytes> mapOfBytes = 5;
   map<string, google.protobuf.StringValue> mapOfStringValues = 6;
+  map<int64, int64> longLookup = 7;
 }
 
 message SimpleWithSnakeCaseMap {
diff --git a/integration/simple/simple.ts b/integration/simple/simple.ts
index 7a35e3d16..f2329834f 100644
--- a/integration/simple/simple.ts
+++ b/integration/simple/simple.ts
@@ -194,6 +194,7 @@ export interface SimpleWithMap {
   mapOfTimestamps: { [key: string]: Date };
   mapOfBytes: { [key: string]: Uint8Array };
   mapOfStringValues: { [key: string]: string | undefined };
+  longLookup: { [key: number]: number };
 }
 
 export interface SimpleWithMap_EntitiesByIdEntry {
@@ -226,6 +227,11 @@ export interface SimpleWithMap_MapOfStringValuesEntry {
   value: string | undefined;
 }
 
+export interface SimpleWithMap_LongLookupEntry {
+  key: number;
+  value: number;
+}
+
 export interface SimpleWithSnakeCaseMap {
   entitiesById: { [key: number]: Entity };
 }
@@ -957,6 +963,9 @@ export const SimpleWithMap = {
         SimpleWithMap_MapOfStringValuesEntry.encode({ key: key as any, value }, writer.uint32(50).fork()).ldelim();
       }
     });
+    Object.entries(message.longLookup).forEach(([key, value]) => {
+      SimpleWithMap_LongLookupEntry.encode({ key: key as any, value }, writer.uint32(58).fork()).ldelim();
+    });
     return writer;
   },
 
@@ -970,6 +979,7 @@ export const SimpleWithMap = {
     message.mapOfTimestamps = {};
     message.mapOfBytes = {};
     message.mapOfStringValues = {};
+    message.longLookup = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -1009,6 +1019,12 @@ export const SimpleWithMap = {
             message.mapOfStringValues[entry6.key] = entry6.value;
           }
           break;
+        case 7:
+          const entry7 = SimpleWithMap_LongLookupEntry.decode(reader, reader.uint32());
+          if (entry7.value !== undefined) {
+            message.longLookup[entry7.key] = entry7.value;
+          }
+          break;
         default:
           reader.skipType(tag & 7);
           break;
@@ -1055,6 +1071,12 @@ export const SimpleWithMap = {
         message.mapOfStringValues[key] = value as string | undefined;
       });
     }
+    message.longLookup = {};
+    if (object.longLookup !== undefined && object.longLookup !== null) {
+      Object.entries(object.longLookup).forEach(([key, value]) => {
+        message.longLookup[Number(key)] = Number(value);
+      });
+    }
     return message;
   },
 
@@ -1096,6 +1118,12 @@ export const SimpleWithMap = {
         obj.mapOfStringValues[k] = v;
       });
     }
+    obj.longLookup = {};
+    if (message.longLookup) {
+      Object.entries(message.longLookup).forEach(([k, v]) => {
+        obj.longLookup[k] = v;
+      });
+    }
     return obj;
   },
 
@@ -1149,6 +1177,14 @@ export const SimpleWithMap = {
         }
       });
     }
+    message.longLookup = {};
+    if (object.longLookup !== undefined && object.longLookup !== null) {
+      Object.entries(object.longLookup).forEach(([key, value]) => {
+        if (value !== undefined) {
+          message.longLookup[Number(key)] = Number(value);
+        }
+      });
+    }
     return message;
   },
 };
@@ -1492,6 +1528,62 @@ export const SimpleWithMap_MapOfStringValuesEntry = {
   },
 };
 
+const baseSimpleWithMap_LongLookupEntry: object = { key: 0, value: 0 };
+
+export const SimpleWithMap_LongLookupEntry = {
+  encode(message: SimpleWithMap_LongLookupEntry, writer: Writer = Writer.create()): Writer {
+    if (message.key !== 0) {
+      writer.uint32(8).int64(message.key);
+    }
+    if (message.value !== 0) {
+      writer.uint32(16).int64(message.value);
+    }
+    return writer;
+  },
+
+  decode(input: Reader | Uint8Array, length?: number): SimpleWithMap_LongLookupEntry {
+    const reader = input instanceof Reader ? input : new Reader(input);
+    let end = length === undefined ? reader.len : reader.pos + length;
+    const message = { ...baseSimpleWithMap_LongLookupEntry } as SimpleWithMap_LongLookupEntry;
+    while (reader.pos < end) {
+      const tag = reader.uint32();
+      switch (tag >>> 3) {
+        case 1:
+          message.key = longToNumber(reader.int64() as Long);
+          break;
+        case 2:
+          message.value = longToNumber(reader.int64() as Long);
+          break;
+        default:
+          reader.skipType(tag & 7);
+          break;
+      }
+    }
+    return message;
+  },
+
+  fromJSON(object: any): SimpleWithMap_LongLookupEntry {
+    const message = { ...baseSimpleWithMap_LongLookupEntry } as SimpleWithMap_LongLookupEntry;
+    message.key = object.key !== undefined && object.key !== null ? Number(object.key) : 0;
+    message.value = object.value !== undefined && object.value !== null ? Number(object.value) : 0;
+    return message;
+  },
+
+  toJSON(message: SimpleWithMap_LongLookupEntry): unknown {
+    const obj: any = {};
+    message.key !== undefined && (obj.key = message.key);
+    message.value !== undefined && (obj.value = message.value);
+    return obj;
+  },
+
+  fromPartial(object: DeepPartial<SimpleWithMap_LongLookupEntry>): SimpleWithMap_LongLookupEntry {
+    const message = { ...baseSimpleWithMap_LongLookupEntry } as SimpleWithMap_LongLookupEntry;
+    message.key = object.key ?? 0;
+    message.value = object.value ?? 0;
+    return message;
+  },
+};
+
 const baseSimpleWithSnakeCaseMap: object = {};
 
 export const SimpleWithSnakeCaseMap = {
diff --git a/src/main.ts b/src/main.ts
index ea3744a18..276217339 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -399,16 +399,19 @@ function makeDeepPartial(options: Options, longs: ReturnType<typeof makeLongUtil
   }
 
   const maybeExport = options.exportCommonSymbols ? 'export' : '';
-  const maybeLong = options.forceLong === LongOption.LONG ? code` | ${longs.Long}` : '';
+  // Allow passing longs as numbers or strings, nad we'll convert them
+  const maybeLong =
+    options.forceLong === LongOption.LONG ? code` : T extends ${longs.Long} ? string | number | Long ` : '';
   const keys = options.outputTypeRegistry ? code`Exclude<keyof T, '$type'>` : code`keyof T`;
 
   // Based on the type from ts-essentials
   const DeepPartial = conditionalOutput(
     'DeepPartial',
     code`
-      type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined${maybeLong};
-      ${maybeExport} type DeepPartial<T> = T extends Builtin
+      type Builtin = Date | Function | Uint8Array | string | number | boolean | undefined;
+      ${maybeExport} type DeepPartial<T> =  T extends Builtin
         ? T
+        ${maybeLong}
         : T extends Array<infer U>
         ? Array<DeepPartial<U>>
         : T extends ReadonlyArray<infer U>
@@ -952,6 +955,8 @@ function generateFromJson(ctx: Context, fullName: string, messageDesc: Descripto
               } else {
                 return code`${utils.bytesFromBase64}(${from} as string)`;
               }
+            } else if (isLong(valueType) && options.forceLong === LongOption.LONG) {
+              return code`Long.fromString(${from} as string)`;
             } else if (isEnum(valueType)) {
               return code`${from} as number`;
             } else {
@@ -1061,6 +1066,8 @@ function generateToJson(ctx: Context, fullName: string, messageDesc: DescriptorP
           return code`${from}`;
         } else if (isTimestamp(valueType) && options.useDate === DateOption.TIMESTAMP) {
           return code`${utils.fromTimestamp}(${from}).toISOString()`;
+        } else if (isLong(valueType) && options.forceLong === LongOption.LONG) {
+          return code`${from}.toString()`;
         } else if (isScalar(valueType) || isValueType(ctx, valueType)) {
           return code`${from}`;
         } else {
@@ -1134,7 +1141,9 @@ function generateFromPartial(ctx: Context, fullName: string, messageDesc: Descri
     const fieldName = maybeSnakeToCamel(field.name, options);
 
     const readSnippet = (from: string): Code => {
-      if (
+      if ((isLong(field) || isLongValueType(field)) && options.forceLong === LongOption.LONG) {
+        return code`Long.fromValue(${from})`;
+      } else if (
         isPrimitive(field) ||
         (isTimestamp(field) && (options.useDate === DateOption.DATE || options.useDate === DateOption.STRING)) ||
         isValueType(ctx, field)
@@ -1148,6 +1157,8 @@ function generateFromPartial(ctx: Context, fullName: string, messageDesc: Descri
               return code`${from}`;
             } else if (isEnum(valueType)) {
               return code`${from} as number`;
+            } else if (isLong(valueType) && options.forceLong === LongOption.LONG) {
+              return code`Long.fromValue(${from})`;
             } else {
               const cstr = capitalize(basicTypeName(ctx, valueType).toCodeString());
               return code`${cstr}(${from})`;
@@ -1203,15 +1214,6 @@ function generateFromPartial(ctx: Context, fullName: string, messageDesc: Descri
           message.${oneofName} = { $case: '${fieldName}', ${fieldName}: ${v} };
         }  
       `);
-    } else if ((isLong(field) || isLongValueType(field)) && options.forceLong === LongOption.LONG) {
-      const v = readSnippet(`object.${fieldName}`);
-      const type = basicTypeName(ctx, field);
-      chunks.push(code`if (object.${fieldName} !== undefined && object.${fieldName} !== null) {`);
-      chunks.push(code`message.${fieldName} = ${v} as ${type};`);
-      chunks.push(code`} else {`);
-      const fallback = isWithinOneOf(field) ? 'undefined' : defaultValue(ctx, field);
-      chunks.push(code`message.${fieldName} = ${fallback}`);
-      chunks.push(code`}`);
     } else if (readSnippet(`x`).toCodeString() == 'x') {
       // An optimized case of the else below that works when `readSnippet` returns the plain input
       const fallback = isWithinOneOf(field) ? 'undefined' : defaultValue(ctx, field);