--- a/make/common/MakeBase.gmk	Thu Oct 22 11:12:30 2015 -0700
+++ b/make/common/MakeBase.gmk	Tue Oct 27 13:48:21 2015 +0100
@@ -640,7 +640,8 @@
           $(if $(findstring $(LOG_LEVEL), trace), \
               $(info NewVariable $1: >$(strip $($1))<) \
               $(info OldVariable $1: >$(strip $($1_old))<)) \
-          $(call WriteFile, $1_old:=$($1), $(call DependOnVariableFileName, $1, $2))) \
+          $(call WriteFile, $1_old:=$(call DoubleDollar,$($1)), \
+              $(call DependOnVariableFileName, $1, $2))) \
         $(call DependOnVariableFileName, $1, $2) \
     )