diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index bb96881cad..0fab0a25fd 100644
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -1150,14 +1150,11 @@ mdsync(void)
 		 * The bitmap manipulations are slightly tricky, because we can call
 		 * AbsorbFsyncRequests() inside the loop and that could result in
 		 * bms_add_member() modifying and even re-palloc'ing the bitmapsets.
-		 * This is okay because we unlink each bitmapset from the hashtable
-		 * entry before scanning it.  That means that any incoming fsync
-		 * requests will be processed now if they reach the table before we
-		 * begin to scan their fork.
+		 * So we need to take a copy.
 		 */
 		for (forknum = 0; forknum <= MAX_FORKNUM; forknum++)
 		{
-			Bitmapset  *requests = entry->requests[forknum];
+			Bitmapset  *requests = bms_copy(entry->requests[forknum]);
 			int			segno;
 
 			entry->requests[forknum] = NULL;
@@ -1272,10 +1269,18 @@ mdsync(void)
 					 */
 					if (!FILE_POSSIBLY_DELETED(errno) ||
 						failures > 0)
+					{
+						/*
+						 * We need to merge these unsatisfied requests with
+						 * any others that have arrived since we started.
+						 */
+						entry->requests[forknum] =
+							bms_union(entry->requests[forknum], requests);
 						ereport(ERROR,
 								(errcode_for_file_access(),
 								 errmsg("could not fsync file \"%s\": %m",
 										path)));
+					}
 					else
 						ereport(DEBUG1,
 								(errcode_for_file_access(),