diff --git a/pkgs/by-name/fc/fcitx5-mozc/package.nix b/pkgs/by-name/fc/fcitx5-mozc/package.nix
index 0e7d0c865e44c..f7a9ec71328c0 100644
--- a/pkgs/by-name/fc/fcitx5-mozc/package.nix
+++ b/pkgs/by-name/fc/fcitx5-mozc/package.nix
@@ -8,6 +8,7 @@
   mozc,
   nixosTests,
   pkg-config,
+  protobuf_27,
   python3,
   stdenv,
   unzip,
@@ -15,7 +16,7 @@
 
 buildBazelPackage {
   pname = "fcitx5-mozc";
-  version = "2.30.5544.102";
+  version = "2.30.5544.102"; # make sure to update protobuf if needed
 
   src = fetchFromGitHub {
     owner = "fcitx";
@@ -38,6 +39,9 @@ buildBazelPackage {
   ];
 
   postPatch = ''
+    # replace protobuf with our own
+    rm -r src/third_party/protobuf
+    cp -r ${protobuf_27.src} src/third_party/protobuf
     sed -i -e 's|^\(LINUX_MOZC_SERVER_DIR = \).\+|\1"${mozc}/lib/mozc"|' src/config.bzl
   '';
 
diff --git a/pkgs/by-name/mo/mozc/package.nix b/pkgs/by-name/mo/mozc/package.nix
index a1b0e804f4525..f32de2fd5f625 100644
--- a/pkgs/by-name/mo/mozc/package.nix
+++ b/pkgs/by-name/mo/mozc/package.nix
@@ -4,6 +4,7 @@
   fetchFromGitHub,
   qt6,
   pkg-config,
+  protobuf_27,
   bazel,
   ibus,
   unzip,
@@ -18,7 +19,7 @@ let
 in
 buildBazelPackage rec {
   pname = "mozc";
-  version = "2.30.5544.102";
+  version = "2.30.5544.102"; # make sure to update protobuf if needed
 
   src = fetchFromGitHub {
     owner = "google";
@@ -63,6 +64,9 @@ buildBazelPackage rec {
   bazelTargets = [ "package" ];
 
   postPatch = ''
+    # replace protobuf with our own
+    rm -r src/third_party/protobuf
+    cp -r ${protobuf_27.src} src/third_party/protobuf
     substituteInPlace src/config.bzl \
       --replace-fail "/usr/bin/xdg-open" "${xdg-utils}/bin/xdg-open" \
       --replace-fail "/usr" "$out"