diff --git a/mercurial/transaction.py b/mercurial/transaction.py
--- a/mercurial/transaction.py
+++ b/mercurial/transaction.py
@@ -720,9 +720,8 @@
     entries = []
     backupentries = []
 
-    fp = opener.open(file)
-    lines = fp.readlines()
-    fp.close()
+    with opener.open(file) as fp:
+        lines = fp.readlines()
     for l in lines:
         try:
             f, o = l.split(b'\0')