diff -uNr a/bitcoin/src/main.cpp b/bitcoin/src/main.cpp
--- a/bitcoin/src/main.cpp 1f0735d2cee2f9ca2a177aead4ecc7a1371d59c4375aedb172ee99c28b02fa28e664decec9580a510bfca4738d85e377fb74396fe4979b75adbe1a3ec92b01c9
+++ b/bitcoin/src/main.cpp 8d726cc72e81befff25d5872e757975c5ee538a6f51a930493fff9b435e4458c736401907fa5d589368cb4a4862614e6fe16ea30cfd568184916733289477a1b
@@ -1877,6 +1877,9 @@
             return error("message getdata size() = %d", vInv.size());
         }
 
+        // Counter of bytes sent in response to this 'getdata' command
+        unsigned int sentBytes = 0;
+
         BOOST_FOREACH(const CInv& inv, vInv)
         {
             if (fShutdown)
@@ -1891,6 +1894,17 @@
                 {
                     CBlock block;
                     block.ReadFromDisk((*mi).second);
+
+                    // Add block's size to sentBytes, and determine if reached limit
+                    sentBytes += block.GetSerializeSize(SER_NETWORK);
+                    if (sentBytes >= SendBufferSize())
+                    {
+                      printf("getdata (block) may not transmit %u bytes\n", sentBytes);
+                      pfrom->Misbehaving(20);
+                      break;
+                    }
+
+                    // Limit not reached, so permitted to send block
                     pfrom->PushMessage("block", block);
 
                     // Trigger them to send a getblocks request for the next batch of inventory