diff --git a/node/src/test/kotlin/net/corda/node/services/statemachine/RetryFlowMockTest.kt b/node/src/test/kotlin/net/corda/node/services/statemachine/RetryFlowMockTest.kt
index e30462d2bf..a3bb5d520a 100644
--- a/node/src/test/kotlin/net/corda/node/services/statemachine/RetryFlowMockTest.kt
+++ b/node/src/test/kotlin/net/corda/node/services/statemachine/RetryFlowMockTest.kt
@@ -126,7 +126,9 @@ class RetryFlowMockTest {
         ReceiveFlow3.lock.release()
         assertTrue(expectedMessagesSent.await(20, TimeUnit.SECONDS))
         assertEquals(3, messagesSent.size)
-        assertNull(messagesSent.last().senderUUID)
+        // CORDA-4045: We can't be sure that the last message sent will be the last we record, so
+        // instead check we have exactly one message (the first) with sender UUID
+        assertNotNull(messagesSent.singleOrNull { it.senderUUID != null })
     }
 
     @Test(timeout=300_000)