--- a/common.mk
+++ b/common.mk
@@ -17,7 +17,7 @@
 # fully made.
 .DELETE_ON_ERROR:
 
-GCC_WARNINGS = -Wall -W -Wno-uninitialized -Wundef -Wimplicit \
+GCC_WARNINGS = -Wall -W -Wno-uninitialized -Wundef \
   -Wno-unknown-pragmas
   # We need -Wwrite-strings after we fix all the missing consts
   #
@@ -27,7 +27,7 @@
   # on -Wuninitialized for all the others.
 
 GCC_C_WARNINGS = $(GCC_WARNINGS) \
-  -Wmissing-declarations -Wstrict-prototypes -Wmissing-prototypes
+  -Wmissing-declarations -Wstrict-prototypes -Wmissing-prototypes -Wimplicit
 
 GCC_CXX_WARNINGS = $(GCC_WARNINGS)  -Wsynth