diff --git a/core/config.mk b/core/config.mk
index d701f04..66c8afb 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -35,9 +35,9 @@
 # only has an effect on python 2.6 and above.
 export PYTHONDONTWRITEBYTECODE := 1
 
-ifneq ($(GREP_OPTIONS),)
+ifneq ($(filter --color=always, $(GREP_OPTIONS)),)
 $(warning The build system needs unmodified output of grep.)
-$(error Please unset your $$GREP_OPTIONS.)
+$(error Please remove --color=always from your  $$GREP_OPTIONS)
 endif
 
 # Standard source directories.