diff --git a/src/Makefile.in.E3SM b/src/Makefile.in.E3SM
index ab44240fb6..ebe00f2206 100644
--- a/src/Makefile.in.E3SM
+++ b/src/Makefile.in.E3SM
@@ -67,7 +67,7 @@ ifeq ($(compile_threaded), TRUE)
     override CPPFLAGS += -DMPAS_OPENMP
 endif
 
-ifeq ($(GEN_F90), TRUE)
+ifeq "$(GEN_F90)" "true"
     override CPPFLAGS += -Uvector
 endif