diff --git a/tools/ci/test_build_system_cmake.sh b/tools/ci/test_build_system_cmake.sh
index ea5bc2e8c3..65e02539bb 100755
--- a/tools/ci/test_build_system_cmake.sh
+++ b/tools/ci/test_build_system_cmake.sh
@@ -692,6 +692,7 @@ endmenu\n" >> ${IDF_PATH}/Kconfig
     rm -f log.txt
 
     print_status "Build fails if partitions don't fit in flash"
+    clean_build_dir
     sed -i.bak "s/CONFIG_ESPTOOLPY_FLASHSIZE.\+//" sdkconfig  # remove all flashsize config
     echo "CONFIG_ESPTOOLPY_FLASHSIZE_1MB=y" >> sdkconfig     # introduce undersize flash
     ( idf.py build 2>&1 | grep "does not fit in configured flash size 1MB" ) || failure "Build didn't fail with expected flash size failure message"