diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -2584,7 +2584,7 @@ def cat(ui, repo, ctx, matcher, prefix, 
     # Don't warn about "missing" files that are really in subrepos
     def badfn(path, msg):
         for subpath in ctx.substate:
-            if path.startswith(subpath):
+            if path.startswith(subpath + '/'):
                 return
         matcher.bad(path, msg)
 
diff --git a/tests/test-subrepo.t b/tests/test-subrepo.t
--- a/tests/test-subrepo.t
+++ b/tests/test-subrepo.t
@@ -60,6 +60,9 @@ Subrepopath which overlaps with filepath
   $ hg remove -S snot/file
   not removing snot/file: file is untracked
   [1]
+  $ hg cat snot/filenot
+  snot/filenot: no such file in rev 7cf8cfea66e4
+  [1]
   $ rm -r snot
 
 Revert subrepo and test subrepo fileset keyword: