diff --git a/mozilla/modules/libmar/src/Makefile.in b/mozilla/modules/libmar/src/Makefile.in
index 1594b6ad5aa..fa8e255231a 100644
--- a/mozilla/modules/libmar/src/Makefile.in
+++ b/mozilla/modules/libmar/src/Makefile.in
@@ -71,3 +71,7 @@ ifdef HOST_NSPR_MDCPUCFG
 HOST_CFLAGS     += -DMDCPUCFG=$(HOST_NSPR_MDCPUCFG)
 endif
 endif
+
+# The intermediate (.ii/.s) files for host and target can have the same name...
+# disable parallel builds
+.NOTPARALLEL: