diff --git a/CLOBBER b/CLOBBER
index b9b501c611de0..f04b62fe51492 100644
--- a/CLOBBER
+++ b/CLOBBER
@@ -22,4 +22,4 @@
 # changes to stick? As of bug 928195, this shouldn't be necessary! Please
 # don't change CLOBBER for WebIDL changes any more.
 
-Bug 1120369 - Needed a CLOBBER on at least Linux and OSX.
+Bug 870366 - Blacklisting PREF_JS_EXPORTS in Makefile.ins (because of 852814)
diff --git a/config/baseconfig.mk b/config/baseconfig.mk
index d4d8081c5b0a0..dd4af0d901ef0 100644
--- a/config/baseconfig.mk
+++ b/config/baseconfig.mk
@@ -90,6 +90,7 @@ _MOZBUILD_EXTERNAL_VARIABLES := \
   NO_DIST_INSTALL \
   OS_LIBS \
   PARALLEL_DIRS \
+  PREF_JS_EXPORTS \
   PROGRAM \
   PYTHON_UNIT_TESTS \
   RESOURCE_FILES \