diff --git a/tests/package-mac-tests.sh b/tests/package-mac-tests.sh
index 86bc89467f..b3ff5765d1 100755
--- a/tests/package-mac-tests.sh
+++ b/tests/package-mac-tests.sh
@@ -62,7 +62,8 @@ if test -n "$INCLUDE_XAMARIN_LEGACY"; then
 fi
 TEST_SUITES+=(build-monotouch-test)
 
-if test -n "$BUILD_REVISION"; then
+# Don't build in parallel in CI, it fails randomly due to trying to write to the same files.
+if test -z "$BUILD_REVISION"; then
 	MAKE_FLAGS=-j
 fi