--- a/build/moz-automation.mk
+++ b/build/moz-automation.mk
@@ -97,16 +97,20 @@ AUTOMATION_EXTRA_CMDLINE-check = -k
 # We need the log from make upload to grep it for urls in order to set
 # properties.
 AUTOMATION_EXTRA_CMDLINE-upload = 2>&1 | tee $(AUTOMATION_UPLOAD_OUTPUT)
 
 # Note: We have to force -j1 here, at least until bug 1036563 is fixed.
 AUTOMATION_EXTRA_CMDLINE-l10n-check = -j1
 AUTOMATION_EXTRA_CMDLINE-pretty-l10n-check = -j1
 
+# And force -j1 here until bug 1077670 is fixed.
+AUTOMATION_EXTRA_CMDLINE-package-tests = -j1
+AUTOMATION_EXTRA_CMDLINE-pretty-package-tests = -j1
+
 # The commands only run if the corresponding MOZ_AUTOMATION_* variable is
 # enabled. This means, for example, if we enable MOZ_AUTOMATION_UPLOAD, then
 # 'buildsymbols' will only run if MOZ_AUTOMATION_BUILD_SYMBOLS is also set.
 # However, the target automation/buildsymbols will still be executed in this
 # case because it is a prerequisite of automation/upload.
 define automation_commands
 $(call BUILDSTATUS,TIER_START $1)
 @$(MAKE) $1 $(AUTOMATION_EXTRA_CMDLINE-$1)