diff --git a/vendor/postgres b/vendor/postgres
index ea5a673983..167196910d 160000
--- a/vendor/postgres
+++ b/vendor/postgres
@@ -1 +1 @@
-Subproject commit ea5a673983ac0d1e055b8da99d3dcca348cecc49
+Subproject commit 167196910d6f41466c82793bcf14bfe442468776
diff --git a/walkeeper/src/wal_service.rs b/walkeeper/src/wal_service.rs
index 69632e3c28..5570781123 100644
--- a/walkeeper/src/wal_service.rs
+++ b/walkeeper/src/wal_service.rs
@@ -1023,7 +1023,14 @@ impl Connection {
                     }
                 }
             }
-            let send_size = min((end_pos - start_pos) as usize, MAX_SEND_SIZE);
+            let xlogoff = XLogSegmentOffset(start_pos, wal_seg_size) as usize;
+
+            // How much to read and send in message? We cannot cross the WAL file
+            // boundary, and we don't want send more than MAX_SEND_SIZE.
+            let send_size = (end_pos - start_pos) as usize;
+            let send_size = min(send_size, wal_seg_size - xlogoff);
+            let send_size = min(send_size, MAX_SEND_SIZE);
+
             let msg_size = LIBPQ_HDR_SIZE + XLOG_HDR_SIZE + send_size;
             let data_start = LIBPQ_HDR_SIZE + XLOG_HDR_SIZE;
             let data_end = data_start + send_size;