diff --git a/mempool/v1/mempool.go b/mempool/v1/mempool.go
index 2e83dc74b..d04fe1ad3 100644
--- a/mempool/v1/mempool.go
+++ b/mempool/v1/mempool.go
@@ -129,7 +129,18 @@ func (txmp *TxMempool) SizeBytes() int64 { return atomic.LoadInt64(&txmp.txsByte
 //
 // The caller must hold an exclusive mempool lock (by calling txmp.Lock) before
 // calling FlushAppConn.
-func (txmp *TxMempool) FlushAppConn() error { return txmp.proxyAppConn.FlushSync() }
+func (txmp *TxMempool) FlushAppConn() error {
+	// N.B.: We have to issue the call outside the lock so that its callback can
+	// fire.  It's safe to do this, the flush will block until complete.
+	//
+	// We could just not require the caller to hold the lock at all, but the
+	// semantics of the Mempool interface require the caller to hold it, and we
+	// can't change that without disrupting existing use.
+	txmp.mtx.Unlock()
+	defer txmp.mtx.Lock()
+
+	return txmp.proxyAppConn.FlushSync()
+}
 
 // EnableTxsAvailable enables the mempool to trigger events when transactions
 // are available on a block by block basis.