--- a/Makefile.in
+++ b/Makefile.in
@@ -221,32 +221,37 @@ endif
 
 default all::
 	$(call BUILDSTATUS,TIERS $(TIERS) $(if $(MOZ_AUTOMATION),$(MOZ_AUTOMATION_TIERS)))
 
 # PGO build target.
 profiledbuild::
 	$(call BUILDSTATUS,TIERS pgo_profile_generate pgo_package pgo_profile pgo_clobber pgo_profile_use)
 	$(call BUILDSTATUS,TIER_START pgo_profile_generate)
-	$(MAKE) MOZ_PROFILE_GENERATE=1 MOZ_PGO_INSTRUMENTED=1
+	$(MAKE) default MOZ_PROFILE_GENERATE=1 MOZ_PGO_INSTRUMENTED=1
 	$(call BUILDSTATUS,TIER_FINISH pgo_profile_generate)
 	$(call BUILDSTATUS,TIER_START pgo_package)
 	$(MAKE) package MOZ_PGO_INSTRUMENTED=1 MOZ_INTERNAL_SIGNING_FORMAT= MOZ_EXTERNAL_SIGNING_FORMAT=
 	rm -f jarlog/en-US.log
 	$(call BUILDSTATUS,TIER_FINISH pgo_package)
 	$(call BUILDSTATUS,TIER_START pgo_profile)
-	MOZ_PGO_INSTRUMENTED=1 JARLOG_FILE=jarlog/en-US.log EXTRA_TEST_ARGS=10 $(MAKE) pgo-profile-run
+	$(MAKE) pgo-profile-run MOZ_PGO_INSTRUMENTED=1 JARLOG_FILE=jarlog/en-US.log EXTRA_TEST_ARGS=10
 	$(call BUILDSTATUS,TIER_FINISH pgo_profile)
 	$(call BUILDSTATUS,TIER_START pgo_clobber)
 	$(MAKE) maybe_clobber_profiledbuild
 	$(call BUILDSTATUS,TIER_FINISH pgo_clobber)
 	$(call BUILDSTATUS,TIER_START pgo_profile_use)
-	$(MAKE) MOZ_PROFILE_USE=1
+	$(MAKE) default MOZ_PROFILE_USE=1
 	$(call BUILDSTATUS,TIER_FINISH pgo_profile_use)
 
+# Change default target to PGO build if PGO is enabled.
+ifdef MOZ_PGO
+OVERRIDE_DEFAULT_GOAL := profiledbuild
+endif
+
 include $(topsrcdir)/config/rules.mk
 
 ifdef SCCACHE_VERBOSE_STATS
 default::
 	-$(CCACHE) --show-stats --stats-format=json > sccache-stats.json
 	@echo "===SCCACHE STATS==="
 	-$(CCACHE) --show-stats
 	@echo "==================="

--- a/client.mk
+++ b/client.mk
@@ -81,37 +81,33 @@ define CR
 
 endef
 
 # As $(shell) doesn't preserve newlines, use sed to replace them with an
 # unlikely sequence (||), which is then replaced back to newlines by make
 # before evaluation. $(shell) replacing newlines with spaces, || is always
 # followed by a space (since sed doesn't remove newlines), except on the
 # last line, so replace both '|| ' and '||'.
-# Also, make MOZ_PGO available to mozconfig when passed on make command line.
-MOZCONFIG_CONTENT := $(subst ||,$(CR),$(subst || ,$(CR),$(shell MOZ_PGO=$(MOZ_PGO) $(TOPSRCDIR)/mach environment --format=client.mk | sed 's/$$/||/')))
+MOZCONFIG_CONTENT := $(subst ||,$(CR),$(subst || ,$(CR),$(shell $(TOPSRCDIR)/mach environment --format=client.mk | sed 's/$$/||/')))
 $(eval $(MOZCONFIG_CONTENT))
 
 export FOUND_MOZCONFIG
 
 # As '||' was used as a newline separator, it means it's not occurring in
 # lines themselves. It can thus safely be used to replaces normal spaces,
 # to then replace newlines with normal spaces. This allows to get a list
 # of mozconfig output lines.
 MOZCONFIG_OUT_LINES := $(subst $(CR), ,$(subst $(NULL) $(NULL),||,$(MOZCONFIG_CONTENT)))
 # Filter-out comments from those lines.
 START_COMMENT = \#
 MOZCONFIG_OUT_FILTERED := $(filter-out $(START_COMMENT)%,$(MOZCONFIG_OUT_LINES))
 
 ifdef AUTOCLOBBER
 export AUTOCLOBBER=1
 endif
-ifdef MOZ_PGO
-export MOZ_PGO
-endif
 
 ifdef MOZ_PARALLEL_BUILD
   MOZ_MAKE_FLAGS := $(filter-out -j%,$(MOZ_MAKE_FLAGS))
   MOZ_MAKE_FLAGS += -j$(MOZ_PARALLEL_BUILD)
 endif
 
 # Automatically add -jN to make flags if not defined. N defaults to number of cores.
 ifeq (,$(findstring -j,$(MOZ_MAKE_FLAGS)))
@@ -285,17 +281,17 @@ ifneq (,$(CONFIG_STATUS))
 $(OBJDIR)/config/autoconf.mk: $(TOPSRCDIR)/config/autoconf.mk.in
 	$(PYTHON) $(OBJDIR)/config.status -n --file=$(OBJDIR)/config/autoconf.mk
 endif
 
 ####################################
 # Build it
 
 build::  $(OBJDIR)/Makefile $(OBJDIR)/config.status
-	+$(MOZ_MAKE) $(if $(MOZ_PGO),profiledbuild)
+	+$(MOZ_MAKE)
 
 ####################################
 # Other targets
 
 # Pass these target onto the real build system
 $(OBJDIR_TARGETS):: $(OBJDIR)/Makefile $(OBJDIR)/config.status
 	+$(MOZ_MAKE) $@
 

--- a/python/mozbuild/mozbuild/test/backend/test_build.py
+++ b/python/mozbuild/mozbuild/test/backend/test_build.py
@@ -29,16 +29,17 @@ BASE_SUBSTS = [
 ]
 
 
 class TestBuild(unittest.TestCase):
     def setUp(self):
         self._old_env = dict(os.environ)
         os.environ.pop('MOZCONFIG', None)
         os.environ.pop('MOZ_OBJDIR', None)
+        os.environ.pop('MOZ_PGO', None)
 
     def tearDown(self):
         os.environ.clear()
         os.environ.update(self._old_env)
 
     @contextmanager
     def do_test_backend(self, *backends, **kwargs):
         topobjdir = mkdtemp()