diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index dcb4cf249c..48efe15e82 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -325,10 +325,13 @@ BackgroundWriterMain(void)
 
 			/*
 			 * Only log if enough time has passed and interesting records have
-			 * been inserted since the last snapshot.
+			 * been inserted since the last snapshot.  Have to compare with <=
+			 * instead of < because GetLastImportantRecPtr() points at the
+			 * start of a record, whereas last_snapshot_lsn points just past
+			 * the end of the record.
 			 */
 			if (now >= timeout &&
-				last_snapshot_lsn < GetLastImportantRecPtr())
+				last_snapshot_lsn <= GetLastImportantRecPtr())
 			{
 				last_snapshot_lsn = LogStandbySnapshot();
 				last_snapshot_ts = now;
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index fe9041f748..d12db0d5a7 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -611,7 +611,8 @@ CheckArchiveTimeout(void)
 	{
 		/*
 		 * Switch segment only when "important" WAL has been logged since the
-		 * last segment switch.
+		 * last segment switch (last_switch_lsn points to end of segment
+		 * switch occurred in).
 		 */
 		if (GetLastImportantRecPtr() > last_switch_lsn)
 		{