diff --git a/lib/Script.js b/lib/Script.js
index 37bcf8e..85f1772 100644
--- a/lib/Script.js
+++ b/lib/Script.js
@@ -110,6 +110,7 @@ function isSmallIntOp(opcode) {
 Script.prototype.isMultiSig = function() {
   return (this.chunks.length > 3 &&
     isSmallIntOp(this.chunks[0]) &&
+    Buffer.isBuffer(this.chunks[1]) &&
     isSmallIntOp(this.chunks[this.chunks.length - 2]) &&
     this.chunks[this.chunks.length - 1] == Opcode.map.OP_CHECKMULTISIG);
 };