diff --git a/core/base_rules.mk b/core/base_rules.mk
index 180ed0b896..f9a1facb4c 100644
--- a/core/base_rules.mk
+++ b/core/base_rules.mk
@@ -101,9 +101,13 @@ ifneq ($(words $(LOCAL_MODULE_CLASS)),1)
   $(error $(LOCAL_PATH): LOCAL_MODULE_CLASS must contain exactly one word, not "$(LOCAL_MODULE_CLASS)")
 endif
 
-# Add a tag like "_class@APPS" to this module so that we can filter
-# based on the class.
-LOCAL_MODULE_TAGS += _class@$(LOCAL_MODULE_CLASS)
+# Those used to be implicitly ignored, but aren't any more.
+# As of 20100110 there are no apps with the user tag.
+ifeq ($(LOCAL_MODULE_CLASS),APPS)
+  ifneq ($(filter $(LOCAL_MODULE_TAGS),user),)
+    $(warning user tag on app $(LOCAL_MODULE) at $(LOCAL_PATH) - add your app to core.mk instead)
+  endif
+endif
 
 LOCAL_MODULE_PATH := $(strip $(LOCAL_MODULE_PATH))
 ifeq ($(LOCAL_MODULE_PATH),)
diff --git a/core/main.mk b/core/main.mk
index 5e318f56bb..96019c0d74 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -447,7 +447,7 @@ include $(ONE_SHOT_MAKEFILE)
 # modules as a side-effect.  Do this after including ONE_SHOT_MAKEFILE
 # so that the modules will be installed in the same place they
 # would have been with a normal make.
-CUSTOM_MODULES := $(sort $(call get-tagged-modules,$(ALL_MODULE_TAGS),))
+CUSTOM_MODULES := $(sort $(call get-tagged-modules,$(ALL_MODULE_TAGS)))
 FULL_BUILD :=
 # Stub out the notice targets, which probably aren't defined
 # when using ONE_SHOT_MAKEFILE.
@@ -549,7 +549,7 @@ else
 endif
 # Use tags to get the non-APPS user modules.  Use the product
 # definition files to get the APPS user modules.
-user_MODULES := $(sort $(call get-tagged-modules,user,_class@APPS restricted))
+user_MODULES := $(sort $(call get-tagged-modules,user,restricted))
 user_MODULES := $(user_MODULES) $(user_PACKAGES)
 
 eng_MODULES := $(sort $(call get-tagged-modules,eng,restricted))