--- a/client.mk
+++ b/client.mk
@@ -86,16 +86,19 @@ ifneq (,$(findstring mingw,$(CONFIG_GUES
 
 # check for CRLF line endings
 ifneq (0,$(shell $(PERL) -e 'binmode(STDIN); while (<STDIN>) { if (/\r/) { print "1"; exit } } print "0"' < $(TOPSRCDIR)/client.mk))
 $(error This source tree appears to have Windows-style line endings. To \
 convert it to Unix-style line endings, check \
 "https://developer.mozilla.org/en-US/docs/Developer_Guide/Mozilla_build_FAQ\#Win32-specific_questions" \
 for a workaround of this issue.)
 endif
+
+# Set this for baseconfig.mk
+HOST_OS_ARCH=WINNT
 endif
 
 ####################################
 # Load mozconfig Options
 
 # See build pages, http://www.mozilla.org/build/ for how to set up mozconfig.
 
 define CR
@@ -162,16 +165,19 @@ OBJDIR_TARGETS = install export libs cle
 
 #######################################################################
 # Rules
 
 # The default rule is build
 build::
 	$(MAKE) -f $(TOPSRCDIR)/client.mk $(if $(MOZ_PGO),profiledbuild,realbuild) CREATE_MOZCONFIG_JSON=
 
+# Include baseconfig.mk for its $(MAKE) validation.
+include $(TOPSRCDIR)/config/baseconfig.mk
+
 # Define mkdir
 include $(TOPSRCDIR)/config/makefiles/makeutils.mk
 include $(TOPSRCDIR)/config/makefiles/autotargets.mk
 
 # Create a makefile containing the mk_add_options values from mozconfig,
 # but only do so when OBJDIR is defined (see further above).
 ifdef MOZ_BUILD_PROJECTS
 ifdef MOZ_CURRENT_PROJECT