diff --git a/rules.mak b/rules.mak
index d1ff311254..4a8f464940 100644
--- a/rules.mak
+++ b/rules.mak
@@ -1,4 +1,6 @@
 
+COMMA := ,
+
 # Don't use implicit rules or variables
 # we have explicit rules for everything
 MAKEFLAGS += -rR