diff --git a/tests/scripts/all-core.sh b/tests/scripts/all-core.sh
index 013e892..8377659 100644
--- a/tests/scripts/all-core.sh
+++ b/tests/scripts/all-core.sh
@@ -371,6 +371,8 @@
               -iname CMakeCache.txt -o \
               -path './cmake/*.cmake' \) -exec rm -f {} \+
     # Remove Makefiles generated by in-tree CMake builds
+    # (Not all files will exist in all branches, but that's OK.)
+    rm -f 3rdparty/Makefile 3rdparty/*/Makefile
     rm -f pkgconfig/Makefile framework/Makefile
     rm -f include/Makefile programs/!(fuzz)/Makefile
     rm -f tf-psa-crypto/Makefile tf-psa-crypto/include/Makefile