diff --git a/Makefile b/Makefile
index 10799fb..e58aef0 100644
--- a/Makefile
+++ b/Makefile
@@ -48,7 +48,7 @@ INCLUDES=-I${incdir}
 ifeq ("$(HAVEPLUS)","true")
   HAVEPLUS=-DHAVE_PLUS
 else
-  HAVEPLUS=""
+  HAVEPLUS=
 endif
 
 ifeq ($(F90),ifort)