diff --git a/test/functional/p2p_instantsend.py b/test/functional/p2p_instantsend.py
index 8dd14eb35cd7..7f4066f3e40d 100755
--- a/test/functional/p2p_instantsend.py
+++ b/test/functional/p2p_instantsend.py
@@ -3,6 +3,8 @@
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+from test_framework.messages import msg_qsendrecsigs
+from test_framework.p2p import P2PInterface
 from test_framework.test_framework import DashTestFramework
 from test_framework.util import assert_equal, assert_raises_rpc_error, force_finish_mnsync
 
@@ -12,6 +14,24 @@
 Tests InstantSend functionality (prevent doublespend for unconfirmed transactions)
 '''
 
+class RecSigsObserver(P2PInterface):
+    """Non-MN peer that opts in to recsigs and records every ISDLOCK inv it sees."""
+
+    def __init__(self):
+        super().__init__()
+        self.isdlock_inv_seen = False
+
+    def send_qsendrecsigs(self, wants_recsigs=True):
+        self.send_message(msg_qsendrecsigs(wants_recsigs))
+
+    def on_inv(self, message):
+        for inv in message.inv:
+            # MSG_ISDLOCK inv type, see src/protocol.h
+            if inv.type == 31:
+                self.isdlock_inv_seen = True
+        super().on_inv(message)
+
+
 class InstantSendTest(DashTestFramework):
     def add_options(self, parser):
         self.add_wallet_options(parser)
@@ -36,6 +56,7 @@ def run_test(self):
 
         self.test_mempool_doublespend()
         self.test_block_doublespend()
+        self.test_isdlock_relayed_to_recsigs_observer()
         self.test_instantsend_after_restart()
 
     def test_block_doublespend(self):
@@ -131,6 +152,27 @@ def test_mempool_doublespend(self):
         # mine more blocks
         self.generate(self.nodes[0], 2)
 
+    def test_isdlock_relayed_to_recsigs_observer(self):
+        self.log.info("Non-MN peer started with -watchquorums must still get ISDLOCK invs")
+        observers = []
+        for mn in self.mninfo:
+            node = mn.get_node(self)
+            obs = node.add_p2p_connection(RecSigsObserver())
+            obs.send_qsendrecsigs(True)
+            obs.sync_with_ping()
+            observers.append((node, obs))
+
+        txid = self.nodes[0].sendtoaddress(self.nodes[0].getnewaddress(), 1)
+        self.wait_for_instantlock(txid)
+        for _, obs in observers:
+            obs.sync_with_ping()
+
+        assert any(obs.isdlock_inv_seen for _, obs in observers), \
+            "non-MN peer with QSENDRECSIGS got no MSG_ISDLOCK inv"
+
+        for node, _ in observers:
+            node.disconnect_p2ps()
+
     def test_instantsend_after_restart(self):
         self.log.info("Testing InstantSend works after full restart without new blocks")
 
diff --git a/test/functional/test_framework/messages.py b/test/functional/test_framework/messages.py
index 1bddb79f12f2..cbc792c9248e 100755
--- a/test/functional/test_framework/messages.py
+++ b/test/functional/test_framework/messages.py
@@ -2447,6 +2447,23 @@ def __repr__(self):
         return "msg_qsigshare(sigShares=%d)" % (len(self.sig_shares))
 
 
+class msg_qsendrecsigs:
+    __slots__ = ("wants_recsigs",)
+    msgtype = b"qsendrecsigs"
+
+    def __init__(self, wants_recsigs=True):
+        self.wants_recsigs = wants_recsigs
+
+    def deserialize(self, f):
+        self.wants_recsigs = bool(struct.unpack("<?", f.read(1))[0])
+
+    def serialize(self):
+        return struct.pack("<?", self.wants_recsigs)
+
+    def __repr__(self):
+        return f"msg_qsendrecsigs(wants_recsigs={self.wants_recsigs})"
+
+
 class msg_qwatch:
     __slots__ = ()
     msgtype = b"qwatch"
diff --git a/test/functional/test_framework/p2p.py b/test/functional/test_framework/p2p.py
index d0d79f5ebc8e..22a085590003 100755
--- a/test/functional/test_framework/p2p.py
+++ b/test/functional/test_framework/p2p.py
@@ -69,6 +69,7 @@
     msg_pong,
     msg_qdata,
     msg_qgetdata,
+    msg_qsendrecsigs,
     msg_sendaddrv2,
     msg_sendcmpct,
     msg_sendheaders,
@@ -177,7 +178,7 @@
     b"qjustify": None,
     b"qpcommit": None,
     b"qrinfo": None,
-    b"qsendrecsigs": None,
+    b"qsendrecsigs": msg_qsendrecsigs,
     b"qsigrec": None,
     b"qsigsesann": None,
     b"qsigshare": None,
@@ -621,6 +622,7 @@ def on_isdlock(self, message): pass
     def on_platformban(self, message): pass
     def on_qgetdata(self, message): pass
     def on_qdata(self, message): pass
+    def on_qsendrecsigs(self, message): pass
     def on_qwatch(self, message): pass
 
     def on_verack(self, message): pass