diff --git a/Tools/ChangeLog b/Tools/ChangeLog
index b9f775d..a6b6c10 100644
--- a/Tools/ChangeLog
+++ b/Tools/ChangeLog
@@ -1,3 +1,17 @@
+2019-12-04  Fujii Hironori  <Hironori.Fujii@sony.com>
+
+        run-javascriptcore-tests is failing to run testmasm of 64bit AppleWin on Buildbot
+        https://bugs.webkit.org/show_bug.cgi?id=204869
+
+        Reviewed by Per Arne Vollan.
+
+        testmasm is compiled only when DEVELOPER_MODE.
+        Enable DEVELOPER_MODE for all 64bit Windows builds.
+
+        * Scripts/webkitdirs.pm:
+        (generateBuildSystemFromCMakeProject): Replaced "isFTW() || isWinCairo()" with isWin64()
+        in the condition of enabling DEVELOPER_MODE.
+
 2019-12-04  Jonathan Bedard  <jbedard@apple.com>
 
         results.webkit.org: Decrease ttl for archives
diff --git a/Tools/Scripts/webkitdirs.pm b/Tools/Scripts/webkitdirs.pm
index 0653970..6408593 100755
--- a/Tools/Scripts/webkitdirs.pm
+++ b/Tools/Scripts/webkitdirs.pm
@@ -2273,7 +2273,7 @@
     push @args, '-DSHOW_BINDINGS_GENERATION_PROGRESS=1' unless ($willUseNinja && -t STDOUT);
 
     # Some ports have production mode, but build-webkit should always use developer mode.
-    push @args, "-DDEVELOPER_MODE=ON" if isFTW() || isGtk() || isJSCOnly() || isWPE() || isWinCairo();
+    push @args, "-DDEVELOPER_MODE=ON" if isGtk() || isJSCOnly() || isWPE() || isWin64();
 
     if (architecture() eq "x86_64" && shouldBuild32Bit()) {
         # CMAKE_LIBRARY_ARCHITECTURE is needed to get the right .pc