diff --git a/Makefile b/Makefile
index 4527dc2..d342502 100644
--- a/Makefile
+++ b/Makefile
@@ -1290,7 +1290,7 @@
 	@echo  '		1: warnings which may be relevant and do not occur too often'
 	@echo  '		2: warnings which occur quite often but may still be relevant'
 	@echo  '		3: more obscure warnings, can most likely be ignored'
-
+	@echo  '		Multiple levels can be combined with W=12 or W=123'
 	@echo  ''
 	@echo  'Execute "make" or "make all" to build all targets marked with [*] '
 	@echo  'For further info see the ./README file'
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 9fb19c0..f133641 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -60,6 +60,8 @@
 # $(call cc-option, -W...) handles gcc -W.. options which
 # are not supported by all versions of the compiler
 ifdef KBUILD_ENABLE_EXTRA_GCC_CHECKS
+warning-  := $(empty)
+
 warning-1 := -Wextra -Wunused -Wno-unused-parameter
 warning-1 += -Wmissing-declarations
 warning-1 += -Wmissing-format-attribute
@@ -86,9 +88,11 @@
 warning-3 += $(call cc-option, -Wpacked-bitfield-compat)
 warning-3 += $(call cc-option, -Wvla)
 
-warning := $(warning-$(KBUILD_ENABLE_EXTRA_GCC_CHECKS))
+warning := $(warning-$(findstring 1, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
+warning += $(warning-$(findstring 2, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
+warning += $(warning-$(findstring 3, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
 
-ifeq ("$(warning)","")
+ifeq ("$(strip $(warning))","")
         $(error W=$(KBUILD_ENABLE_EXTRA_GCC_CHECKS) is unknown)
 endif