diff --git a/src/interfaces/libpq/fe-misc.c b/src/interfaces/libpq/fe-misc.c
index 660cdec93c..5a74a95968 100644
--- a/src/interfaces/libpq/fe-misc.c
+++ b/src/interfaces/libpq/fe-misc.c
@@ -541,7 +541,19 @@ pqPutMsgEnd(PGconn *conn)
 
 	if (conn->outCount >= 8192)
 	{
-		int			toSend = conn->outCount - (conn->outCount % 8192);
+		int			toSend = conn->outCount;
+
+		/*
+		 * Normally we only send full 8K blocks.  However, if we don't present
+		 * the last partial block we can trigger pg_GSS_write's "failed to
+		 * retransmit all data" failure, since rounding toSend down could
+		 * result in not presenting some data that we did present on an
+		 * earlier try.  The full-block heuristic is pretty useless anyway
+		 * when encrypting, since encryption overhead will throw off the
+		 * number.  Hence, in GSSAPI mode just send all we have.
+		 */
+		if (!conn->gssenc)
+			toSend -= toSend % 8192;
 
 		if (pqSendSome(conn, toSend) < 0)
 			return EOF;