diff --git a/src/malloc/malloc.c b/src/malloc/malloc.c
index ee6f170b1839d9dde5990cceaaf43d2d6c21a5eb..46cc21fb7b54ed95310c51e7ac0ee6a285ff5532 100644
--- a/src/malloc/malloc.c
+++ b/src/malloc/malloc.c
@@ -333,7 +333,7 @@ void *malloc(size_t n)
 	if (adjust_size(&n) < 0) return 0;
 
 	if (n > MMAP_THRESHOLD) {
-		size_t len = n + PAGE_SIZE - 1 & -PAGE_SIZE;
+		size_t len = n + OVERHEAD + PAGE_SIZE - 1 & -PAGE_SIZE;
 		char *base = __mmap(0, len, PROT_READ|PROT_WRITE,
 			MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
 		if (base == (void *)-1) return 0;