fixes #29624

build/win32/code.iss

@@ -800,20 +800,23 @@ var
   AltArch: String;
 begin
   Result := True;
-  RegKey := 'SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\' + copy('{#IncompatibleAppId}', 2, 38) + '_is1';
-
-  if '{#Arch}' = 'ia32' then begin
-    Result := not RegKeyExists(HKLM64, RegKey);
-    ThisArch := '32';
-    AltArch := '64';
-  end else begin
-    Result := not RegKeyExists(HKLM32, RegKey);
-    ThisArch := '64';
-    AltArch := '32';
-  end;
 
-  if not Result then begin
-    MsgBox('Please uninstall {#NameShort} ' + AltArch + 'bits before installing this ' + ThisArch + 'bits version.', mbInformation, MB_OK);
+  if IsWin64 then begin
+    RegKey := 'SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\' + copy('{#IncompatibleAppId}', 2, 38) + '_is1';
+
+    if '{#Arch}' = 'ia32' then begin
+      Result := not RegKeyExists(HKLM64, RegKey);
+      ThisArch := '32';
+      AltArch := '64';
+    end else begin
+      Result := not RegKeyExists(HKLM32, RegKey);
+      ThisArch := '64';
+      AltArch := '32';
+    end;
+
+    if not Result then begin
+      MsgBox('Please uninstall {#NameShort} ' + AltArch + 'bits before installing this ' + ThisArch + 'bits version.', mbInformation, MB_OK);
+    end;
   end;
 end;