diff --git a/newlib/libc/stdlib/nano-mallocr.c b/newlib/libc/stdlib/nano-mallocr.c
index 18a16c924..6fb08a616 100644
--- a/newlib/libc/stdlib/nano-mallocr.c
+++ b/newlib/libc/stdlib/nano-mallocr.c
@@ -40,6 +40,7 @@
 #if DEBUG
 #include <assert.h>
 #else
+#undef assert
 #define assert(x) ((void)0)
 #endif