diff --git a/libc/include/malloc.h b/libc/include/malloc.h
index 412e3f0..db5da04 100644
--- a/libc/include/malloc.h
+++ b/libc/include/malloc.h
@@ -77,6 +77,11 @@
  */
 int malloc_info(int, FILE*) __INTRODUCED_IN(23);
 
+/* mallopt options */
+#define M_DECAY_TIME -100
+
+int mallopt(int, int) __INTRODUCED_IN(26);
+
 __END_DECLS
 
 #endif  /* LIBC_INCLUDE_MALLOC_H_ */