diff --git a/js/src/Makefile.in b/js/src/Makefile.in
index f500ddeb2138..8b7a244a12ab 100644
--- a/js/src/Makefile.in
+++ b/js/src/Makefile.in
@@ -92,7 +92,7 @@ MODULE_OPTIMIZE_FLAGS = -O3 -fstrict-aliasing
 
 # We normally want -fomit-frame-pointer, but we want an explicit
 # -fno-omit-frame-pointer if we're using a sampling profiler.
-ifeq(,$(MOZ_PROFILING))
+ifndef MOZ_PROFILING
 MODULE_OPTIMIZE_FLAGS += -fomit-frame-pointer
 else
 MODULE_OPTIMIZE_FLAGS += -fno-omit-frame-pointer