diff --git a/sys/cbor/Makefile b/sys/cbor/Makefile
index 8e1c52a54e..bd0de57963 100644
--- a/sys/cbor/Makefile
+++ b/sys/cbor/Makefile
@@ -1,7 +1,7 @@
 MODULE = cbor
 
 ifneq ($(shell uname -s),Darwin)
-	CFLAGS += -D_XOPEN_SOURCE=600
+  CFLAGS += -D_XOPEN_SOURCE=600
 endif
 
 include $(RIOTBASE)/Makefile.base