diff --git a/test/run-tests.sh b/test/run-tests.sh
index 8476f368f12ac3f72b63f3f0ba20aabc17b4eb0e..578125241974f41203fee715600e58a3fde6df9a 100755
--- a/test/run-tests.sh
+++ b/test/run-tests.sh
@@ -327,6 +327,7 @@ valid_upgrade_test_p () {
 run_upgrade_tests () {
     cd ${ASDFDIR}
     mkdir -p  build/results
+    rm -f build/*.*f* ## Remove stale FASLs from ASDF 1.x, especially when different implementations have same name
     ASDF_OUTPUT_TRANSLATIONS="(:output-translations (\"${ASDFDIR}\" (\"${ASDFDIR}/build/fasls/\" :implementation \"asdf/\")) (t (\"${ASDFDIR}/build/fasls/\" :implementation \"root/\")) :ignore-inherited-configuration)"
     export ASDF_OUTPUT_TRANSLATIONS
     su=test/script-support.lisp