diff --git a/pkgs/by-name/si/signal-desktop/package.nix b/pkgs/by-name/si/signal-desktop/package.nix
index 2a6c02f481a9..0df70c12eafb 100644
--- a/pkgs/by-name/si/signal-desktop/package.nix
+++ b/pkgs/by-name/si/signal-desktop/package.nix
@@ -112,6 +112,18 @@ stdenv.mkDerivation (finalAttrs: {
     }
   );
 
+  postPatch = ''
+    # The spell checker dictionary URL interpolates the electron version,
+    # however, the official website only provides dictionaries for electron
+    # versions which they vendor into the binary releases. Since we unpin
+    # electron to use the one from nixpkgs the URL may point to nonexistent
+    # resource if the nixpkgs version is different. To fix this we hardcode
+    # the electron version to the declared one here instead of interpolating
+    # it at runtime.
+    substituteInPlace app/updateDefaultSession.ts \
+      --replace-fail "\''${process.versions.electron}" "`jq -r '.devDependencies.electron' < package.json`"
+  '';
+
   pnpmDeps = pnpm.fetchDeps {
     inherit (finalAttrs)
       pname