--- libmalloc/libmalloc-374.120.1/xcodeconfig/libmalloc_xctests.xcconfig
+++ libmalloc/libmalloc-409.81.2/xcodeconfig/libmalloc_xctests.xcconfig
@@ -18,3 +18,5 @@
 
 XCODE_SIGN_IDENTITY = -
 CODE_SIGN_IDENTITY = -
+
+GCC_PREPROCESSOR_DEFINITIONS = MALLOC_BUILDING_XCTESTS