diff --git a/build/jam/HelperRules b/build/jam/HelperRules
index 1dcdfbf5b2..7772fb7dac 100644
--- a/build/jam/HelperRules
+++ b/build/jam/HelperRules
@@ -213,7 +213,7 @@ rule SetIncludePropertiesVariables prefix : suffix
 	# SetIncludePropertiesVariables <prefix> : <suffix> ;
 	#
 	suffix = $(suffix:E=) ;
-	if $($(prefix)_CC_IS_LEGACY_GCC$(suffix)) {
+	if $($(prefix)_CC_IS_LEGACY_GCC$(suffix)) = 1 {
 		$(prefix)_INCLUDES_SEPARATOR$(suffix) = -I- ;
 		$(prefix)_LOCAL_INCLUDES_OPTION$(suffix) = -I ;
 		$(prefix)_SYSTEM_INCLUDES_OPTION$(suffix) = -I ;