diff --git a/.changeset/giant-pears-learn.md b/.changeset/giant-pears-learn.md
new file mode 100644
index 00000000000..e71b8b917b0
--- /dev/null
+++ b/.changeset/giant-pears-learn.md
@@ -0,0 +1,5 @@
+---
+"@apollo/client": patch
+---
+
+Fix import extension in masking entry point.
diff --git a/.size-limits.json b/.size-limits.json
index c072f5c094e..54bce409ebd 100644
--- a/.size-limits.json
+++ b/.size-limits.json
@@ -1,4 +1,4 @@
 {
-  "dist/apollo-client.min.cjs": 41614,
+  "dist/apollo-client.min.cjs": 41613,
   "import { ApolloClient, InMemoryCache, HttpLink } from \"dist/index.js\" (production)": 34349
 }
diff --git a/src/masking/types.ts b/src/masking/types.ts
index ebf8cdd4ad4..b50617d6d64 100644
--- a/src/masking/types.ts
+++ b/src/masking/types.ts
@@ -5,7 +5,7 @@ import type {
   RemoveFragmentName,
   RemoveMaskedMarker,
   UnwrapFragmentRefs,
-} from "./internal/types.ts";
+} from "./internal/types.js";
 import type { Prettify } from "../utilities/index.js";
 
 export interface DataMasking {}