diff --git a/httpx/_utils.py b/httpx/_utils.py
index 1f64deedcd..1e1570ee7f 100644
--- a/httpx/_utils.py
+++ b/httpx/_utils.py
@@ -67,7 +67,11 @@ def primitive_value_to_str(value: "PrimitiveData") -> str:
         return "false"
     elif value is None:
         return ""
-    return str(value)
+    elif isinstance(value, (str, float, int)):
+        return str(value)
+    raise TypeError(
+        f"Expected str, int, float, bool, or None. Got {type(value).__name__!r}."
+    )
 
 
 def is_known_encoding(encoding: str) -> bool:
diff --git a/tests/models/test_queryparams.py b/tests/models/test_queryparams.py
index 29b2ca634d..cbb487bbc6 100644
--- a/tests/models/test_queryparams.py
+++ b/tests/models/test_queryparams.py
@@ -87,6 +87,13 @@ def test_empty_query_params():
     assert str(q) == "a="
 
 
+def test_invalid_query_params():
+    with pytest.raises(
+        TypeError, match=r"Expected str, int, float, bool, or None. Got 'bytes'."
+    ):
+        httpx.QueryParams({"a": b"bytes"})
+
+
 def test_queryparam_update_is_hard_deprecated():
     q = httpx.QueryParams("a=123")
     with pytest.raises(RuntimeError):