diff --git a/rules.mak b/rules.mak
index d1ff311254948b2f61d91e6eb0befd2fa620e157..4a8f464940bc3b2c611d4a70b760bc5ff06f5954 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