diff --git a/lib/net/packets.js b/lib/net/packets.js
index c760a18e..bf746d07 100644
--- a/lib/net/packets.js
+++ b/lib/net/packets.js
@@ -977,6 +977,8 @@ GetBlocksPacket.prototype.getSize = function getSize() {
 GetBlocksPacket.prototype.toWriter = function toWriter(bw) {
   var i;
 
+  assert(this.locator.length <= 50000, 'Too many block hashes.');
+
   bw.writeU32(this.version);
   bw.writeVarint(this.locator.length);
 
@@ -1011,6 +1013,8 @@ GetBlocksPacket.prototype.fromReader = function fromReader(br) {
 
   count = br.readVarint();
 
+  assert(count <= 50000, 'Too many block hashes.');
+
   for (i = 0; i < count; i++)
     this.locator.push(br.readHash('hex'));