diff --git a/Makefile.system b/Makefile.system
index 7686c938b..6cf65c7bd 100644
--- a/Makefile.system
+++ b/Makefile.system
@@ -189,7 +189,7 @@ ifeq ($(C_COMPILER), INTEL)
 CCOMMON_OPT    += -wd981
 endif
 
-ifdef USE_OPENMP
+ifeq ($(USE_OPENMP), 1)
 ifeq ($(C_COMPILER), GCC)
 CCOMMON_OPT    += -fopenmp
 endif