diff --git a/doc/release-notes.md b/doc/release-notes.md
--- a/doc/release-notes.md
+++ b/doc/release-notes.md
@@ -6,3 +6,6 @@
  - Added parameter `include_removed` to `listsinceblock` for better tracking of
    transactions during a reorg. See `bitcoin-cli help listsinceblock` for more
    details.
+ - `listsinceblock` will now throw an error if an unknown `blockhash` argument
+   value is passed, instead of returning a list of all wallet transactions since
+   the genesis block.
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -2238,19 +2238,20 @@
     int target_confirms = 1;
     isminefilter filter = ISMINE_SPENDABLE;
 
-    if (!request.params[0].isNull()) {
+    if (!request.params[0].isNull() && !request.params[0].get_str().empty()) {
         uint256 blockId;
 
         blockId.SetHex(request.params[0].get_str());
         BlockMap::iterator it = mapBlockIndex.find(blockId);
-        if (it != mapBlockIndex.end()) {
-            paltindex = pindex = it->second;
-            if (chainActive[pindex->nHeight] != pindex) {
-                // the block being asked for is a part of a deactivated chain;
-                // we don't want to depend on its perceived height in the block
-                // chain, we want to instead use the last common ancestor
-                pindex = chainActive.FindFork(pindex);
-            }
+        if (it == mapBlockIndex.end()) {
+            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found");
+        }
+        paltindex = pindex = it->second;
+        if (chainActive[pindex->nHeight] != pindex) {
+            // the block being asked for is a part of a deactivated chain;
+            // we don't want to depend on its perceived height in the block
+            // chain, we want to instead use the last common ancestor
+            pindex = chainActive.FindFork(pindex);
         }
     }
 
diff --git a/test/functional/wallet_listsinceblock.py b/test/functional/wallet_listsinceblock.py
--- a/test/functional/wallet_listsinceblock.py
+++ b/test/functional/wallet_listsinceblock.py
@@ -4,7 +4,7 @@
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 from test_framework.test_framework import BitcoinTestFramework
-from test_framework.util import assert_equal
+from test_framework.util import assert_equal, assert_array_result, assert_raises_rpc_error
 
 
 class ListSinceBlockTest (BitcoinTestFramework):
@@ -17,10 +17,43 @@
         self.nodes[2].generate(101)
         self.sync_all()
 
+        self.test_no_blockhash()
+        self.test_invalid_blockhash()
         self.test_reorg()
         self.test_double_spend()
         self.test_double_send()
 
+    def test_no_blockhash(self):
+        txid = self.nodes[2].sendtoaddress(self.nodes[0].getnewaddress(), 1)
+        blockhash, = self.nodes[2].generate(1)
+        self.sync_all()
+
+        txs = self.nodes[0].listtransactions()
+        assert_array_result(txs, {"txid": txid}, {
+            "category": "receive",
+            "amount": 1,
+            "blockhash": blockhash,
+            "confirmations": 1,
+        })
+        assert_equal(
+            self.nodes[0].listsinceblock(),
+            {"lastblock": blockhash,
+             "removed": [],
+             "transactions": txs})
+        assert_equal(
+            self.nodes[0].listsinceblock(""),
+            {"lastblock": blockhash,
+             "removed": [],
+             "transactions": txs})
+
+    def test_invalid_blockhash(self):
+        assert_raises_rpc_error(-5, "Block not found", self.nodes[0].listsinceblock,
+                                "42759cde25462784395a337460bde75f58e73d3f08bd31fdc3507cbac856a2c4")
+        assert_raises_rpc_error(-5, "Block not found", self.nodes[0].listsinceblock,
+                                "0000000000000000000000000000000000000000000000000000000000000000")
+        assert_raises_rpc_error(-5, "Block not found", self.nodes[0].listsinceblock,
+                                "invalid-hex")
+
     def test_reorg(self):
         '''
         `listsinceblock` did not behave correctly when handed a block that was