diff --git a/src/sds.c b/src/sds.c
index eafa13c29..ff633c8bc 100644
--- a/src/sds.c
+++ b/src/sds.c
@@ -248,16 +248,23 @@ sds sdsMakeRoomFor(sds s, size_t addlen) {
 sds sdsRemoveFreeSpace(sds s) {
     void *sh, *newsh;
     char type, oldtype = s[-1] & SDS_TYPE_MASK;
-    int hdrlen;
+    int hdrlen, oldhdrlen = sdsHdrSize(oldtype);
     size_t len = sdslen(s);
-    sh = (char*)s-sdsHdrSize(oldtype);
+    sh = (char*)s-oldhdrlen;
 
+    /* Check what would be the minimum SDS header that is just good enough to
+     * fit this string. */
     type = sdsReqType(len);
     hdrlen = sdsHdrSize(type);
-    if (oldtype==type) {
-        newsh = s_realloc(sh, hdrlen+len+1);
+
+    /* If the type is the same, or at least a large enough type is still
+     * required, we just realloc(), letting the allocator to do the copy
+     * only if really needed. Otherwise if the change is huge, we manually
+     * reallocate the string to use the different header type. */
+    if (oldtype==type || type > SDS_TYPE_8) {
+        newsh = s_realloc(sh, oldhdrlen+len+1);
         if (newsh == NULL) return NULL;
-        s = (char*)newsh+hdrlen;
+        s = (char*)newsh+oldhdrlen;
     } else {
         newsh = s_malloc(hdrlen+len+1);
         if (newsh == NULL) return NULL;