--- a/build/mozconfig.cache
+++ b/build/mozconfig.cache
@@ -55,17 +55,17 @@ else
     case "$master" in
     *use1.mozilla.com*|*usw2.mozilla.com*)
         mk_add_options "export SCCACHE_NAMESERVER=169.254.169.253"
         ;;
     esac
     ac_add_options "--with-compiler-wrapper=python2.7 $topsrcdir/sccache/sccache.py"
     mk_add_options MOZ_PREFLIGHT_ALL+=build/sccache.mk
     mk_add_options MOZ_POSTFLIGHT_ALL+=build/sccache.mk
-    UPLOAD_EXTRA_FILES="$UPLOAD_EXTRA_FILES sccache.log.gz"
+    mk_add_options "export UPLOAD_EXTRA_FILES+=sccache.log.gz"
     case "$platform" in
     win*)
         # sccache supports a special flag to create depfiles.
         export _DEPEND_CFLAGS='-deps$(MDDEPDIR)/$(@F).pp'
         # Windows builds have a default wrapper that needs to be overridden
         mk_add_options "export CC_WRAPPER="
         mk_add_options "export CXX_WRAPPER="
         # For now, sccache doesn't support separate PDBs so force debug info to be

--- a/client.mk
+++ b/client.mk
@@ -190,16 +190,22 @@ MOZCONFIG_MK_LINES := $(filter export||%
 	$(if $(MOZCONFIG_MK_LINES),( $(foreach line,$(MOZCONFIG_MK_LINES), echo '$(subst ||, ,$(line))';) )) > $@
 
 # Include that makefile so that it is created. This should not actually change
 # the environment since MOZCONFIG_CONTENT, which MOZCONFIG_OUT_LINES derives
 # from, has already been eval'ed.
 include $(OBJDIR)/.mozconfig.mk
 endif
 
+# UPLOAD_EXTRA_FILES is appended to and exported from mozconfig, which makes
+# submakes as well as configure add even more to that, so just unexport it
+# for submakes to pick it from .mozconfig.mk and for configure to pick it
+# from mach environment.
+unexport UPLOAD_EXTRA_FILES
+
 # Print out any options loaded from mozconfig.
 all realbuild clean distclean export libs install realclean::
 ifneq (,$(strip $(MOZCONFIG_OUT_FILTERED)))
 	$(info Adding client.mk options from $(FOUND_MOZCONFIG):)
 	$(foreach line,$(MOZCONFIG_OUT_FILTERED),$(info $(NULL) $(NULL) $(NULL) $(NULL) $(subst ||, ,$(line))))
 endif
 
 # Windows equivalents

--- a/configure.in
+++ b/configure.in
@@ -8890,18 +8890,16 @@ fi
 
 MOZ_CONFIG_ICU()
 
 if test -z "$JS_SHARED_LIBRARY"; then
   AC_DEFINE(MOZ_STATIC_JS)
 fi
 AC_SUBST(JS_SHARED_LIBRARY)
 
-AC_SUBST(UPLOAD_EXTRA_FILES)
-
 MOZ_CREATE_CONFIG_STATUS()
 
 # No need to run subconfigures when building with LIBXUL_SDK_DIR
 if test "$COMPILE_ENVIRONMENT" -a -z "$LIBXUL_SDK_DIR"; then
   MOZ_SUBCONFIGURE_ICU()
   MOZ_SUBCONFIGURE_FFI()
 fi