diff --git a/CHANGES.md b/CHANGES.md
index 6c00562825..d0656c675a 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -21,6 +21,7 @@ Fixed:
   number of channels.
 - Improved support for unitary minus, fix runtime call of optional
   methods (#3498)
+- Fixed `map.metadata` mutating existing metadata.
 - Fixed reloading loop in playlists with invalid files (#3479)
 - Fixed main HLS playlist codecs when using `mpegts` (#3483)
 - Fixed pop/clicks in crossfade and source with caching (#3318)
diff --git a/src/core/operators/map_metadata.ml b/src/core/operators/map_metadata.ml
index 7a9c3492a6..d74bbaa10f 100644
--- a/src/core/operators/map_metadata.ml
+++ b/src/core/operators/map_metadata.ml
@@ -63,8 +63,10 @@ class map_metadata source rewrite_f insert_missing update strip =
       List.iter
         (fun (t, m) ->
           if t >= p then (
+            let m = Hashtbl.copy m in
             self#rewrite m;
-            if strip && Hashtbl.length m = 0 then Frame.free_metadata buf t))
+            if strip && Hashtbl.length m = 0 then Frame.free_metadata buf t
+            else Frame.set_metadata buf t m))
         (Frame.get_all_metadata buf)
   end