--- old/make/linux/makefiles/gcc.make	2019-08-28 12:02:29.000000000 -0700
+++ new/make/linux/makefiles/gcc.make	2019-08-28 12:02:29.000000000 -0700
@@ -211,7 +211,7 @@
   WARNINGS_ARE_ERRORS += -Wno-return-type -Wno-empty-body
 endif
 
-WARNING_FLAGS = -Wpointer-arith -Wsign-compare -Wundef -Wunused-function -Wunused-value
+WARNING_FLAGS = -Wpointer-arith -Wsign-compare -Wundef -Wunused-function -Wunused-value -Wreturn-type
 
 ifeq ($(USE_CLANG),)
   # Since GCC 4.3, -Wconversion has changed its meanings to warn these implicit