diff --git a/hgext/remotefilelog/shallowutil.py b/hgext/remotefilelog/shallowutil.py
--- a/hgext/remotefilelog/shallowutil.py
+++ b/hgext/remotefilelog/shallowutil.py
@@ -237,9 +237,9 @@
             # v0, str(int(size)) is the header
             size = int(header)
     except ValueError:
-        raise RuntimeError("unexpected remotefilelog header: illegal format")
+        raise RuntimeError(r"unexpected remotefilelog header: illegal format")
     if size is None:
-        raise RuntimeError("unexpected remotefilelog header: no size found")
+        raise RuntimeError(r"unexpected remotefilelog header: no size found")
     return index + 1, size, flags
 
 def buildfileblobheader(size, flags, version=None):