Index: /trunk/Config.kmk
===================================================================
--- /trunk/Config.kmk	(revision 29367)
+++ /trunk/Config.kmk	(revision 29368)
@@ -1277,5 +1277,5 @@
 VBOX_GCC_WARN     ?= -Wall $(VBOX_GCC_Wextra) $(VBOX_GCC_Wno-missing-field-initializers) -Wno-unused -Wno-trigraphs $(VBOX_GCC_fdiagnostics-show-option)
 VBOX_GCC_PEDANTIC_CXX ?= -pedantic -Wshadow $(VBOX_GCC_WARN) -Wno-long-long
-VBOX_GCC_PEDANTIC_C   ?= -pedantic -Wshadow $(VBOX_GCC_WARN) -Wno-long-long -Wmissing-prototypes -Wstrict-prototypes -Wmissing-declarations
+VBOX_GCC_PEDANTIC_C   ?= -pedantic -Wshadow $(VBOX_GCC_WARN) -Wno-long-long -Wmissing-prototypes -Wstrict-prototypes -Wmissing-declarations -Werror-implicit-function-declaration
 ifeq ($(KBUILD_TYPE),debug)
  VBOX_GCC_FP     ?= -fno-omit-frame-pointer