diff --git a/sds.c b/sds.c
index 01b00f3..a20ba19 100644
--- a/sds.c
+++ b/sds.c
@@ -90,7 +90,7 @@ sds sdsnewlen(const void *init, size_t initlen) {
     int hdrlen = sdsHdrSize(type);
     unsigned char *fp; /* flags pointer. */
 
-    assert(initlen + hdrlen + 1 > initlen); /* Catch size_t overflow */
+    if (hdrlen+initlen+1 <= initlen) return NULL; /* Catch size_t overflow */
     sh = s_malloc(hdrlen+initlen+1);
     if (sh == NULL) return NULL;
     if (!init)
@@ -207,7 +207,7 @@ sds sdsMakeRoomFor(sds s, size_t addlen) {
     len = sdslen(s);
     sh = (char*)s-sdsHdrSize(oldtype);
     reqlen = newlen = (len+addlen);
-    assert(newlen > len);   /* Catch size_t overflow */
+    if (newlen <= len) return NULL; /* Catch size_t overflow */
     if (newlen < SDS_MAX_PREALLOC)
         newlen *= 2;
     else
@@ -221,7 +221,7 @@ sds sdsMakeRoomFor(sds s, size_t addlen) {
     if (type == SDS_TYPE_5) type = SDS_TYPE_8;
 
     hdrlen = sdsHdrSize(type);
-    assert(hdrlen + newlen + 1 > reqlen);  /* Catch size_t overflow */
+    if (hdrlen+newlen+1 <= reqlen) return NULL; /* Catch size_t overflow */
     if (oldtype==type) {
         newsh = s_realloc(sh, hdrlen+newlen+1);
         if (newsh == NULL) return NULL;