diff --git a/src/backend/port/unix_latch.c b/src/backend/port/unix_latch.c
index 409beaed8d..e64282c210 100644
--- a/src/backend/port/unix_latch.c
+++ b/src/backend/port/unix_latch.c
@@ -172,6 +172,10 @@ WaitLatch(volatile Latch *latch, int wakeEvents, long timeout)
 /*
  * Like WaitLatch, but with an extra socket argument for WL_SOCKET_*
  * conditions.
+ *
+ * When waiting on a socket, WL_SOCKET_READABLE *must* be included in
+ * 'wakeEvents'; WL_SOCKET_WRITEABLE is optional.  The reason for this is
+ * that EOF and error conditions are reported only via WL_SOCKET_READABLE.
  */
 int
 WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
@@ -195,6 +199,8 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
 		wakeEvents &= ~(WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE);
 
 	Assert(wakeEvents != 0);	/* must have at least one wake event */
+	/* Cannot specify WL_SOCKET_WRITEABLE without WL_SOCKET_READABLE */
+	Assert((wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE)) != WL_SOCKET_WRITEABLE);
 
 	if ((wakeEvents & WL_LATCH_SET) && latch->owner_pid != MyProcPid)
 		elog(ERROR, "cannot wait on a latch owned by another process");
@@ -295,7 +301,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
 		if ((wakeEvents & WL_SOCKET_READABLE) &&
 			(pfds[0].revents & (POLLIN | POLLHUP | POLLERR | POLLNVAL)))
 		{
-			/* data available in socket */
+			/* data available in socket, or EOF/error condition */
 			result |= WL_SOCKET_READABLE;
 		}
 		if ((wakeEvents & WL_SOCKET_WRITEABLE) &&
@@ -373,7 +379,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
 		}
 		if ((wakeEvents & WL_SOCKET_READABLE) && FD_ISSET(sock, &input_mask))
 		{
-			/* data available in socket */
+			/* data available in socket, or EOF */
 			result |= WL_SOCKET_READABLE;
 		}
 		if ((wakeEvents & WL_SOCKET_WRITEABLE) && FD_ISSET(sock, &output_mask))
diff --git a/src/backend/port/win32_latch.c b/src/backend/port/win32_latch.c
index 62800ad66f..05b34269b5 100644
--- a/src/backend/port/win32_latch.c
+++ b/src/backend/port/win32_latch.c
@@ -106,6 +106,8 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
 		wakeEvents &= ~(WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE);
 
 	Assert(wakeEvents != 0);	/* must have at least one wake event */
+	/* Cannot specify WL_SOCKET_WRITEABLE without WL_SOCKET_READABLE */
+	Assert((wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE)) != WL_SOCKET_WRITEABLE);
 
 	if ((wakeEvents & WL_LATCH_SET) && latch->owner_pid != MyProcPid)
 		elog(ERROR, "cannot wait on a latch owned by another process");