diff --git a/src/sds.c b/src/sds.c
index 50369de1bf1601b0bdc1e642f16b476d5a037e3b..0a635701ad9bf1c6d2ac3fbb67552dd9814d9eb8 100644
--- a/src/sds.c
+++ b/src/sds.c
@@ -107,7 +107,11 @@ static sds sdsMakeRoomFor(sds s, size_t addlen) {
     if (free >= addlen) return s;
     len = sdslen(s);
     sh = (void*) (s-(sizeof(struct sdshdr)));
-    newlen = (len+addlen)*2;
+    newlen = (len+addlen);
+    if (newlen < SDS_MAX_PREALLOC)
+        newlen *= 2;
+    else
+        newlen += SDS_MAX_PREALLOC;
     newsh = zrealloc(sh, sizeof(struct sdshdr)+newlen+1);
 #ifdef SDS_ABORT_ON_OOM
     if (newsh == NULL) sdsOomAbort();
diff --git a/src/sds.h b/src/sds.h
index aa6f1781e9b09c6ba34d5856ef089c939730aa00..902e7c65983d82b5b09dc912cb9a938d22809b11 100644
--- a/src/sds.h
+++ b/src/sds.h
@@ -31,6 +31,8 @@
 #ifndef __SDS_H
 #define __SDS_H
 
+#define SDS_MAX_PREALLOC (1024*1024)
+
 #include <sys/types.h>
 #include <stdarg.h>