diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -1763,27 +1763,20 @@
     int blockcount = 30 * 24 * 60 * 60 /
                      config.GetChainParams().GetConsensus().nPowTargetSpacing;
 
-    bool havehash = !request.params[1].isNull();
-    uint256 hash;
-    if (havehash) {
-        hash = uint256S(request.params[1].get_str());
-    }
-
-    {
+    if (request.params[1].isNull()) {
         LOCK(cs_main);
-        if (havehash) {
-            auto it = mapBlockIndex.find(hash);
-            if (it == mapBlockIndex.end()) {
-                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY,
-                                   "Block not found");
-            }
-            pindex = it->second;
-            if (!chainActive.Contains(pindex)) {
-                throw JSONRPCError(RPC_INVALID_PARAMETER,
-                                   "Block is not in main chain");
-            }
-        } else {
-            pindex = chainActive.Tip();
+        pindex = chainActive.Tip();
+    } else {
+        uint256 hash = uint256S(request.params[1].get_str());
+        LOCK(cs_main);
+        auto it = mapBlockIndex.find(hash);
+        if (it == mapBlockIndex.end()) {
+            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found");
+        }
+        pindex = it->second;
+        if (!chainActive.Contains(pindex)) {
+            throw JSONRPCError(RPC_INVALID_PARAMETER,
+                               "Block is not in main chain");
         }
     }
 
diff --git a/test/functional/rpc_blockchain.py b/test/functional/rpc_blockchain.py
--- a/test/functional/rpc_blockchain.py
+++ b/test/functional/rpc_blockchain.py
@@ -79,6 +79,29 @@
     def _test_getchaintxstats(self):
         self.log.info("Test getchaintxstats")
 
+        # Test `getchaintxstats` invalid extra parameters
+        assert_raises_rpc_error(
+            -1, 'getchaintxstats', self.nodes[0].getchaintxstats, 0, '', 0)
+
+        # Test `getchaintxstats` invalid `nblocks`
+        assert_raises_rpc_error(
+            -1, "JSON value is not an integer as expected", self.nodes[0].getchaintxstats, '')
+        assert_raises_rpc_error(
+            -8, "Invalid block count: should be between 0 and the block's height - 1", self.nodes[0].getchaintxstats, -1)
+        assert_raises_rpc_error(-8, "Invalid block count: should be between 0 and the block's height - 1", self.nodes[
+                                0].getchaintxstats, self.nodes[0].getblockcount())
+
+        # Test `getchaintxstats` invalid `blockhash`
+        assert_raises_rpc_error(
+            -1, "JSON value is not a string as expected", self.nodes[0].getchaintxstats, blockhash=0)
+        assert_raises_rpc_error(
+            -5, "Block not found", self.nodes[0].getchaintxstats, blockhash='0')
+        blockhash = self.nodes[0].getblockhash(200)
+        self.nodes[0].invalidateblock(blockhash)
+        assert_raises_rpc_error(
+            -8, "Block is not in main chain", self.nodes[0].getchaintxstats, blockhash=blockhash)
+        self.nodes[0].reconsiderblock(blockhash)
+
         chaintxstats = self.nodes[0].getchaintxstats(1)
         # 200 txs plus genesis tx
         assert_equal(chaintxstats['txcount'], 201)
@@ -111,10 +134,6 @@
         assert('window_interval' not in chaintxstats)
         assert('txrate' not in chaintxstats)
 
-        assert_raises_rpc_error(
-            -8, "Invalid block count: should be between 0 and the block's height - 1",
-            self.nodes[0].getchaintxstats, 201)
-
     def _test_gettxoutsetinfo(self):
         node = self.nodes[0]
         res = node.gettxoutsetinfo()