diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 5ecf868..c3b708f 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -191,6 +191,7 @@
 
 msg "build: cmake, full config, clang" # ~ 50s
 cleanup
+cp "$CONFIG_H" "$CONFIG_BAK"
 scripts/config.pl full
 scripts/config.pl unset MBEDTLS_MEMORY_BACKTRACE # too slow for tests
 CC=clang cmake -D CMAKE_BUILD_TYPE:String=Check .