diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index b823c159d..7e5f0d608 100644
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -720,7 +720,7 @@ protected:
 
 UniValue submitblock(const JSONRPCRequest& request)
 {
-    if (request.fHelp || request.params.size() < 1 || request.params.size() > 2)
+    if (request.fHelp || request.params.size() < 1 || request.params.size() > 2) {
         throw std::runtime_error(
             "submitblock \"hexdata\" ( \"jsonparametersobject\" )\n"
             "\nAttempts to submit new block to network.\n"
@@ -738,11 +738,17 @@ UniValue submitblock(const JSONRPCRequest& request)
             + HelpExampleCli("submitblock", "\"mydata\"")
             + HelpExampleRpc("submitblock", "\"mydata\"")
         );
+    }
 
     std::shared_ptr<CBlock> blockptr = std::make_shared<CBlock>();
     CBlock& block = *blockptr;
-    if (!DecodeHexBlk(block, request.params[0].get_str()))
+    if (!DecodeHexBlk(block, request.params[0].get_str())) {
         throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "Block decode failed");
+    }
+
+    if (block.vtx.empty() || !block.vtx[0]->IsCoinBase()) {
+        throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "Block does not start with a coinbase");
+    }
 
     uint256 hash = block.GetHash();
     bool fBlockPresent = false;
@@ -751,10 +757,12 @@ UniValue submitblock(const JSONRPCRequest& request)
         BlockMap::iterator mi = mapBlockIndex.find(hash);
         if (mi != mapBlockIndex.end()) {
             CBlockIndex *pindex = mi->second;
-            if (pindex->IsValid(BLOCK_VALID_SCRIPTS))
+            if (pindex->IsValid(BLOCK_VALID_SCRIPTS)) {
                 return "duplicate";
-            if (pindex->nStatus & BLOCK_FAILED_MASK)
+            }
+            if (pindex->nStatus & BLOCK_FAILED_MASK) {
                 return "duplicate-invalid";
+            }
             // Otherwise, we might only have the header - process the block before returning
             fBlockPresent = true;
         }
@@ -772,14 +780,15 @@ UniValue submitblock(const JSONRPCRequest& request)
     RegisterValidationInterface(&sc);
     bool fAccepted = ProcessNewBlock(Params(), blockptr, true, NULL);
     UnregisterValidationInterface(&sc);
-    if (fBlockPresent)
-    {
-        if (fAccepted && !sc.found)
+    if (fBlockPresent) {
+        if (fAccepted && !sc.found) {
             return "duplicate-inconclusive";
+        }
         return "duplicate";
     }
-    if (!sc.found)
+    if (!sc.found) {
         return "inconclusive";
+    }
     return BIP22ValidationResult(sc.state);
 }
 
diff --git a/src/validation.cpp b/src/validation.cpp
index 6ade63398..7eae5fd80 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -2901,9 +2901,11 @@ bool IsWitnessEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& pa
 static int GetWitnessCommitmentIndex(const CBlock& block)
 {
     int commitpos = -1;
-    for (size_t o = 0; o < block.vtx[0]->vout.size(); o++) {
-        if (block.vtx[0]->vout[o].scriptPubKey.size() >= 38 && block.vtx[0]->vout[o].scriptPubKey[0] == OP_RETURN && block.vtx[0]->vout[o].scriptPubKey[1] == 0x24 && block.vtx[0]->vout[o].scriptPubKey[2] == 0xaa && block.vtx[0]->vout[o].scriptPubKey[3] == 0x21 && block.vtx[0]->vout[o].scriptPubKey[4] == 0xa9 && block.vtx[0]->vout[o].scriptPubKey[5] == 0xed) {
-            commitpos = o;
+    if (!block.vtx.empty()) {
+        for (size_t o = 0; o < block.vtx[0]->vout.size(); o++) {
+            if (block.vtx[0]->vout[o].scriptPubKey.size() >= 38 && block.vtx[0]->vout[o].scriptPubKey[0] == OP_RETURN && block.vtx[0]->vout[o].scriptPubKey[1] == 0x24 && block.vtx[0]->vout[o].scriptPubKey[2] == 0xaa && block.vtx[0]->vout[o].scriptPubKey[3] == 0x21 && block.vtx[0]->vout[o].scriptPubKey[4] == 0xa9 && block.vtx[0]->vout[o].scriptPubKey[5] == 0xed) {
+                commitpos = o;
+            }
         }
     }
     return commitpos;