diff --git a/spec/build/testsuites/libtests/malloc04.yml b/spec/build/testsuites/libtests/malloc04.yml
index 4d29a73eeb..1cc88a7c7c 100644
--- a/spec/build/testsuites/libtests/malloc04.yml
+++ b/spec/build/testsuites/libtests/malloc04.yml
@@ -1,6 +1,7 @@
 SPDX-License-Identifier: CC-BY-SA-4.0 OR BSD-2-Clause
 build-type: test-program
-cflags: []
+cflags:
+- -fno-builtin
 copyrights:
 - Copyright (C) 2020 embedded brains GmbH & Co. KG
 cppflags: []
diff --git a/spec/build/testsuites/libtests/malloctest.yml b/spec/build/testsuites/libtests/malloctest.yml
index 8989a9cbae..1a8f1bc981 100644
--- a/spec/build/testsuites/libtests/malloctest.yml
+++ b/spec/build/testsuites/libtests/malloctest.yml
@@ -1,6 +1,7 @@
 SPDX-License-Identifier: CC-BY-SA-4.0 OR BSD-2-Clause
 build-type: test-program
-cflags: []
+cflags:
+- -fno-builtin
 copyrights:
 - Copyright (C) 2020 embedded brains GmbH & Co. KG
 cppflags: []