diff --git a/src/merkleblock.h b/src/merkleblock.h
--- a/src/merkleblock.h
+++ b/src/merkleblock.h
@@ -136,6 +136,12 @@
      */
     uint256 ExtractMatches(std::vector<uint256> &vMatch,
                            std::vector<size_t> &vnIndex);
+
+    /**
+     * Get number of transactions the merkle proof is indicating for
+     * cross-reference with local blockchain knowledge.
+     */
+    uint32_t GetNumTransactions() const { return nTransactions; };
 };
 
 /**
diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -371,7 +371,7 @@
             "generated by gettxoutproof\n"
             "\nResult:\n"
             "[\"txid\"]      (array, strings) The txid(s) which the proof "
-            "commits to, or empty array if the proof is invalid\n");
+            "commits to, or empty array if the proof can not be validated.\n");
     }
 
     CDataStream ssMB(ParseHexV(request.params[0], "proof"), SER_NETWORK,
@@ -391,13 +391,16 @@
     LOCK(cs_main);
 
     const CBlockIndex *pindex = LookupBlockIndex(merkleBlock.header.GetHash());
-    if (!pindex || !chainActive.Contains(pindex)) {
+    if (!pindex || !chainActive.Contains(pindex) || pindex->nTx == 0) {
         throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY,
                            "Block not found in chain");
     }
 
-    for (const uint256 &hash : vMatch) {
-        res.push_back(hash.GetHex());
+    // Check if proof is valid, only add results if so
+    if (pindex->nTx == merkleBlock.txn.GetNumTransactions()) {
+        for (const uint256 &hash : vMatch) {
+            res.push_back(hash.GetHex());
+        }
     }
 
     return res;
diff --git a/test/functional/rpc_txoutproof.py b/test/functional/rpc_txoutproof.py
--- a/test/functional/rpc_txoutproof.py
+++ b/test/functional/rpc_txoutproof.py
@@ -13,6 +13,7 @@
     assert_raises_rpc_error,
     connect_nodes,
 )
+from test_framework.messages import CMerkleBlock, FromHex, ToHex
 
 
 class MerkleBlockTest(BitcoinTestFramework):
@@ -104,6 +105,28 @@
         assert_raises_rpc_error(-5, "Not all transactions found in specified or retrieved block",
                                 self.nodes[2].gettxoutproof, [txid1, txid3])
 
+        # Now we'll try tweaking a proof.
+        proof = self.nodes[3].gettxoutproof([txid1, txid2])
+        assert txid1 in self.nodes[0].verifytxoutproof(proof)
+        assert txid2 in self.nodes[1].verifytxoutproof(proof)
+
+        tweaked_proof = FromHex(CMerkleBlock(), proof)
+
+        # Make sure that our serialization/deserialization is working
+        assert txid1 in self.nodes[2].verifytxoutproof(ToHex(tweaked_proof))
+
+        # Check to see if we can go up the merkle tree and pass this off as a
+        # single-transaction block
+        tweaked_proof.txn.nTransactions = 1
+        tweaked_proof.txn.vHash = [tweaked_proof.header.hashMerkleRoot]
+        tweaked_proof.txn.vBits = [True] + [False]*7
+
+        for n in self.nodes:
+            assert not n.verifytxoutproof(ToHex(tweaked_proof))
+
+        # TODO: try more variants, eg transactions at different depths, and
+        # verify that the proofs are invalid
+
 
 if __name__ == '__main__':
     MerkleBlockTest().main()
diff --git a/test/functional/test_framework/messages.py b/test/functional/test_framework/messages.py
--- a/test/functional/test_framework/messages.py
+++ b/test/functional/test_framework/messages.py
@@ -731,6 +731,54 @@
             self.blockhash, repr(self.transactions))
 
 
+class CPartialMerkleTree():
+    def __init__(self):
+        self.nTransactions = 0
+        self.vHash = []
+        self.vBits = []
+        self.fBad = False
+
+    def deserialize(self, f):
+        self.nTransactions = struct.unpack("<i", f.read(4))[0]
+        self.vHash = deser_uint256_vector(f)
+        vBytes = deser_string(f)
+        self.vBits = []
+        for i in range(len(vBytes) * 8):
+            self.vBits.append(vBytes[i // 8] & (1 << (i % 8)) != 0)
+
+    def serialize(self):
+        r = b""
+        r += struct.pack("<i", self.nTransactions)
+        r += ser_uint256_vector(self.vHash)
+        vBytesArray = bytearray([0x00] * ((len(self.vBits) + 7) // 8))
+        for i in range(len(self.vBits)):
+            vBytesArray[i // 8] |= self.vBits[i] << (i % 8)
+        r += ser_string(bytes(vBytesArray))
+        return r
+
+    def __repr__(self):
+        return "CPartialMerkleTree(nTransactions={}, vHash={}, vBits={})".format(self.nTransactions, repr(self.vHash), repr(self.vBits))
+
+
+class CMerkleBlock():
+    def __init__(self):
+        self.header = CBlockHeader()
+        self.txn = CPartialMerkleTree()
+
+    def deserialize(self, f):
+        self.header.deserialize(f)
+        self.txn.deserialize(f)
+
+    def serialize(self):
+        r = b""
+        r += self.header.serialize()
+        r += self.txn.serialize()
+        return r
+
+    def __repr__(self):
+        return "CMerkleBlock(header={}, txn={})".format(repr(self.header), repr(self.txn))
+
+
 # Objects that correspond to messages on the wire
 class msg_version():
     command = b"version"