diff --git a/coap_config.h.riot b/coap_config.h.riot
index 76e54a5d..a07f5a11 100644
--- a/coap_config.h.riot
+++ b/coap_config.h.riot
@@ -31,7 +31,7 @@
 
 /* Define to 1 if your system has a GNU libc compatible `malloc' function, and
    to 0 otherwise. */
-#define HAVE_MALLOC 0
+#undef HAVE_MALLOC
 
 /* Define to 1 if you have the <memory.h> header file. */
 /* #undef HAVE_MEMORY_H */
@@ -67,7 +67,7 @@
 #define HAVE_STRING_H 1
 
 /* Define to 1 if you have the `strnlen' function. */
-#define HAVE_STRNLEN 1
+/* #undef HAVE_STRNLEN */
 
 /* Define to 1 if you have the `strrchr' function. */
 #define HAVE_STRRCHR 1