diff --git a/pkgs/development/libraries/qt-5/5.15/default.nix b/pkgs/development/libraries/qt-5/5.15/default.nix
index 6334217f7458..80d75b8cf880 100644
--- a/pkgs/development/libraries/qt-5/5.15/default.nix
+++ b/pkgs/development/libraries/qt-5/5.15/default.nix
@@ -196,6 +196,11 @@ let
       ./qtwebengine-darwin-checks.patch
     ];
     qtwebkit = [
+      (fetchpatch {
+        name = "qtwebkit-python39-json.patch";
+        url = "https://github.com/qtwebkit/qtwebkit/commit/78360c01c796b6260bf828bc9c8a0ef73c5132fd.patch";
+        sha256 = "yCX/UL666BPxjnxT6rIsUrJsPcSWHhZwMFJfuHhbkhk=";
+      })
       (fetchpatch {
         name = "qtwebkit-bison-3.7-build.patch";
         url = "https://github.com/qtwebkit/qtwebkit/commit/d92b11fea65364fefa700249bd3340e0cd4c5b31.patch";