diff --git a/src/backend/storage/ipc/shm_mq.c b/src/backend/storage/ipc/shm_mq.c
index e765cea..8e10822 100644
--- a/src/backend/storage/ipc/shm_mq.c
+++ b/src/backend/storage/ipc/shm_mq.c
@@ -777,7 +777,7 @@ shm_mq_send_bytes(shm_mq_handle *mqh, Size nbytes, const void *data,
 			return SHM_MQ_DETACHED;
 		}
 
-		if (available == 0)
+		if (available == 0 && !mqh->mqh_counterparty_attached)
 		{
 			shm_mq_result res;
 
@@ -805,6 +805,13 @@ shm_mq_send_bytes(shm_mq_handle *mqh, Size nbytes, const void *data,
 				mqh->mqh_counterparty_attached = true;
 			}
 
+			/*
+			 * The receiver may have read some data after attaching, so we
+			 * must not wait without rechecking the queue state.
+			 */
+		}
+		else if (available == 0)
+		{
 			/* Let the receiver know that we need them to read some data. */
 			res = shm_mq_notify_receiver(mq);
 			if (res != SHM_MQ_SUCCESS)