diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 1df626b70f..6a32b8455e 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -917,8 +917,8 @@ void PeerLogicValidation::BlockChecked(const CBlock& block, const CValidationSta
 
     int nDoS = 0;
     if (state.IsInvalid(nDoS)) {
-        if (it != mapBlockSource.end() && State(it->second.first)) {
-            assert (state.GetRejectCode() < REJECT_INTERNAL); // Blocks are never rejected with internal reject codes
+        // Don't send reject message with code 0 or an internal reject code.
+        if (it != mapBlockSource.end() && State(it->second.first) && state.GetRejectCode() > 0 && state.GetRejectCode() < REJECT_INTERNAL) {
             CBlockReject reject = {(unsigned char)state.GetRejectCode(), state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), hash};
             State(it->second.first)->rejects.push_back(reject);
             if (nDoS > 0 && it->second.second)
@@ -2348,7 +2348,7 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
             LogPrint("mempoolrej", "%s from peer=%d was not accepted: %s\n", tx.GetHash().ToString(),
                 pfrom->id,
                 FormatStateMessage(state));
-            if (state.GetRejectCode() < REJECT_INTERNAL) // Never send AcceptToMemoryPool's internal codes over P2P
+            if (state.GetRejectCode() > 0 && state.GetRejectCode() < REJECT_INTERNAL) // Never send AcceptToMemoryPool's internal codes over P2P
                 connman.PushMessage(pfrom, msgMaker.Make(NetMsgType::REJECT, strCommand, (unsigned char)state.GetRejectCode(),
                                    state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), inv.hash));
             if (nDoS > 0) {
diff --git a/src/validation.cpp b/src/validation.cpp
index f4095e2ec4..de9fe3bb57 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -2185,7 +2185,7 @@ static bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockInd
     LogPrint("bench", "      - Connect %u transactions: %.2fms (%.3fms/tx, %.3fms/txin) [%.2fs]\n", (unsigned)block.vtx.size(), 0.001 * (nTime3 - nTime2), 0.001 * (nTime3 - nTime2) / block.vtx.size(), nInputs <= 1 ? 0 : 0.001 * (nTime3 - nTime2) / (nInputs-1), nTimeConnect * 0.000001);
 
     if (!control.Wait())
-        return state.DoS(100, false);
+        return state.DoS(100, error("%s: CheckQueue failed", __func__), REJECT_INVALID, "block-validation-failed");
     int64_t nTime4 = GetTimeMicros(); nTimeVerify += nTime4 - nTime2;
     LogPrint("bench", "    - Verify %u txins: %.2fms (%.3fms/txin) [%.2fs]\n", nInputs - 1, 0.001 * (nTime4 - nTime2), nInputs <= 1 ? 0 : 0.001 * (nTime4 - nTime2) / (nInputs-1), nTimeVerify * 0.000001);
 
@@ -3338,10 +3338,12 @@ static bool CheckIndexAgainstCheckpoint(const CBlockIndex* pindexPrev, CValidati
         return true;
 
     int nHeight = pindexPrev->nHeight+1;
-    // Don't accept any forks from the main chain prior to last checkpoint
+    // Don't accept any forks from the main chain prior to last checkpoint.
+    // GetLastCheckpoint finds the last checkpoint in MapCheckpoints that's in our
+    // MapBlockIndex.
     CBlockIndex* pcheckpoint = Checkpoints::GetLastCheckpoint(chainparams.Checkpoints());
     if (pcheckpoint && nHeight < pcheckpoint->nHeight)
-        return state.DoS(100, error("%s: forked chain older than last checkpoint (height %d)", __func__, nHeight));
+        return state.DoS(100, error("%s: forked chain older than last checkpoint (height %d)", __func__, nHeight), REJECT_CHECKPOINT, "bad-fork-prior-to-checkpoint");
 
     return true;
 }
@@ -3471,7 +3473,7 @@ static bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state
         CBlockIndex* pindexPrev = NULL;
         BlockMap::iterator mi = mapBlockIndex.find(block.hashPrevBlock);
         if (mi == mapBlockIndex.end())
-            return state.DoS(10, error("%s: prev block not found", __func__), 0, "bad-prevblk");
+            return state.DoS(10, error("%s: prev block not found", __func__), 0, "prev-blk-not-found");
         pindexPrev = (*mi).second;
         assert(pindexPrev);
 
diff --git a/test/functional/p2p-fullblocktest.py b/test/functional/p2p-fullblocktest.py
index 90ec10758e..f060216860 100755
--- a/test/functional/p2p-fullblocktest.py
+++ b/test/functional/p2p-fullblocktest.py
@@ -404,7 +404,7 @@ class FullBlockTest(ComparisonTestFramework):
 
         # Extend the b26 chain to make sure bitcoind isn't accepting b26
         b27 = block(27, spend=out[7])
-        yield rejected(RejectResult(0, b'bad-prevblk'))
+        yield rejected(False)
 
         # Now try a too-large-coinbase script
         tip(15)
@@ -416,7 +416,7 @@ class FullBlockTest(ComparisonTestFramework):
 
         # Extend the b28 chain to make sure bitcoind isn't accepting b28
         b29 = block(29, spend=out[7])
-        yield rejected(RejectResult(0, b'bad-prevblk'))
+        yield rejected(False)
 
         # b30 has a max-sized coinbase scriptSig.
         tip(23)