diff --git a/Makefile.in b/Makefile.in
index 1a6f004d5c1..ee1da71bde9 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -205,6 +205,21 @@ codesighs:
 # defined in package-name.mk
 export MOZ_SOURCE_STAMP
 
+#XXX: this is a hack, since we don't want to clobber for MSVC
+# PGO support, but we can't do this test in client.mk
+ifneq ($(OS_ARCH)_$(GNU_CC), WINNT_)
+# No point in clobbering if PGO has been explicitly disabled.
+ifndef NO_PROFILE_GUIDED_OPTIMIZE
+maybe_clobber_profiledbuild: clean
+else
+maybe_clobber_profiledbuild:
+endif
+else
+maybe_clobber_profiledbuild:
+endif
+
+.PHONY: maybe_clobber_profiledbuild
+
 # Look for R_386_PC32 relocations in shared libs, these
 # break x86_64 builds and SELinux users.
 ifeq ($(OS_TARGET)_$(TARGET_XPCOM_ABI),Linux_x86-gcc3)
diff --git a/client.mk b/client.mk
index 0e22371c63b..ad6f4b09a1e 100644
--- a/client.mk
+++ b/client.mk
@@ -212,6 +212,7 @@ profiledbuild::
 	$(MAKE) -f $(TOPSRCDIR)/client.mk realbuild MOZ_PROFILE_GENERATE=1
 	$(MAKE) -C $(PGO_OBJDIR) package
 	OBJDIR=${PGO_OBJDIR} JARLOG_DIR=${PGO_OBJDIR}/jarlog/en-US $(PROFILE_GEN_SCRIPT)
+	$(MAKE) -f $(TOPSRCDIR)/client.mk maybe_clobber_profiledbuild
 	$(MAKE) -f $(TOPSRCDIR)/client.mk realbuild MOZ_PROFILE_USE=1
 
 #####################################################
@@ -253,7 +254,7 @@ endif
 # loop through them.
 
 ifeq (,$(MOZ_CURRENT_PROJECT)$(if $(MOZ_BUILD_PROJECTS),,1))
-configure depend realbuild install export libs clean realclean distclean alldep preflight postflight upload sdk::
+configure depend realbuild install export libs clean realclean distclean alldep preflight postflight maybe_clobber_profiledbuild upload sdk::
 	set -e; \
 	for app in $(MOZ_BUILD_PROJECTS); do \
 	  $(MAKE) -f $(TOPSRCDIR)/client.mk $@ MOZ_CURRENT_PROJECT=$$app; \
@@ -353,7 +354,7 @@ realbuild::  $(OBJDIR)/Makefile $(OBJDIR)/config.status
 # Other targets
 
 # Pass these target onto the real build system
-install export libs clean realclean distclean alldep upload sdk:: $(OBJDIR)/Makefile $(OBJDIR)/config.status
+install export libs clean realclean distclean alldep maybe_clobber_profiledbuild upload sdk:: $(OBJDIR)/Makefile $(OBJDIR)/config.status
 	$(MOZ_MAKE) $@
 
 ####################################
@@ -412,4 +413,4 @@ echo-variable-%:
 # in parallel.
 .NOTPARALLEL:
 
-.PHONY: checkout real_checkout depend realbuild build profiledbuild export libs alldep install clean realclean distclean cleansrcdir pull_all build_all clobber clobber_all pull_and_build_all everything configure preflight_all preflight postflight postflight_all upload sdk
+.PHONY: checkout real_checkout depend realbuild build profiledbuild maybe_clobber_profiledbuild export libs alldep install clean realclean distclean cleansrcdir pull_all build_all clobber clobber_all pull_and_build_all everything configure preflight_all preflight postflight postflight_all upload sdk
diff --git a/config/rules.mk b/config/rules.mk
index 29078c9ad1e..726368514ec 100644
--- a/config/rules.mk
+++ b/config/rules.mk
@@ -815,9 +815,6 @@ ifdef SHARED_LIBRARY
 	  $(SHARED_LIBRARY_NAME) $(DIST)/$(MOZ_APP_NAME)
 endif
 endif # SHARED_LIBRARY || PROGRAM
-else  # ! WINNT_
-# Force rebuilding all objects on the second pass
-$(OBJS): FORCE
 endif # WINNT_
 endif # MOZ_PROFILE_USE
 ifdef MOZ_PROFILE_GENERATE
diff --git a/js/src/config/rules.mk b/js/src/config/rules.mk
index 29078c9ad1e..726368514ec 100644
--- a/js/src/config/rules.mk
+++ b/js/src/config/rules.mk
@@ -815,9 +815,6 @@ ifdef SHARED_LIBRARY
 	  $(SHARED_LIBRARY_NAME) $(DIST)/$(MOZ_APP_NAME)
 endif
 endif # SHARED_LIBRARY || PROGRAM
-else  # ! WINNT_
-# Force rebuilding all objects on the second pass
-$(OBJS): FORCE
 endif # WINNT_
 endif # MOZ_PROFILE_USE
 ifdef MOZ_PROFILE_GENERATE