--- a/config/rules.mk
+++ b/config/rules.mk
@@ -49,21 +49,21 @@ INCLUDED_RULES_MK = 1
   XPIDL_FLAGS \
   $(NULL)
 
 ifndef EXTERNALLY_MANAGED_MAKE_FILE
 # Using $(firstword) may not be perfect. But it should be good enough for most
 # scenarios.
 _current_makefile = $(CURDIR)/$(firstword $(MAKEFILE_LIST))
 
-$(foreach var,$(_MOZBUILD_EXTERNAL_VARIABLES),$(if $(filter file override,$(subst $(NULL) ,_,$(origin $(var)))),\
+$(foreach var,$(_MOZBUILD_EXTERNAL_VARIABLES),$(if $($(var)),\
     $(error Variable $(var) is defined in $(_current_makefile). It should only be defined in moz.build files),\
     ))
 
-$(foreach var,$(_DEPRECATED_VARIABLES),$(if $(filter file override,$(subst $(NULL) ,_,$(origin $(var)))),\
+$(foreach var,$(_DEPRECATED_VARIABLES),$(if $($(var)),\
     $(error Variable $(var) is defined in $(_current_makefile). This variable has been deprecated. It does nothing. It must be removed in order to build)\
     ))
 
 ifneq (,$(XPIDLSRCS)$(SDK_XPIDLSRCS))
     $(error XPIDLSRCS and SDK_XPIDLSRCS have been merged and moved to moz.build files as the XPIDL_SOURCES variable. You must move these variables out of $(_current_makefile))
 endif
 
 # Import the automatically generated backend file. If this file doesn't exist,

--- a/js/src/config/rules.mk
+++ b/js/src/config/rules.mk
@@ -49,21 +49,21 @@ INCLUDED_RULES_MK = 1
   XPIDL_FLAGS \
   $(NULL)
 
 ifndef EXTERNALLY_MANAGED_MAKE_FILE
 # Using $(firstword) may not be perfect. But it should be good enough for most
 # scenarios.
 _current_makefile = $(CURDIR)/$(firstword $(MAKEFILE_LIST))
 
-$(foreach var,$(_MOZBUILD_EXTERNAL_VARIABLES),$(if $(filter file override,$(subst $(NULL) ,_,$(origin $(var)))),\
+$(foreach var,$(_MOZBUILD_EXTERNAL_VARIABLES),$(if $($(var)),\
     $(error Variable $(var) is defined in $(_current_makefile). It should only be defined in moz.build files),\
     ))
 
-$(foreach var,$(_DEPRECATED_VARIABLES),$(if $(filter file override,$(subst $(NULL) ,_,$(origin $(var)))),\
+$(foreach var,$(_DEPRECATED_VARIABLES),$(if $($(var)),\
     $(error Variable $(var) is defined in $(_current_makefile). This variable has been deprecated. It does nothing. It must be removed in order to build)\
     ))
 
 ifneq (,$(XPIDLSRCS)$(SDK_XPIDLSRCS))
     $(error XPIDLSRCS and SDK_XPIDLSRCS have been merged and moved to moz.build files as the XPIDL_SOURCES variable. You must move these variables out of $(_current_makefile))
 endif
 
 # Import the automatically generated backend file. If this file doesn't exist,