diff --git a/hgext/fsmonitor/__init__.py b/hgext/fsmonitor/__init__.py
--- a/hgext/fsmonitor/__init__.py
+++ b/hgext/fsmonitor/__init__.py
@@ -207,8 +207,8 @@
     if isinstance(ex, watchmanclient.Unavailable):
         # experimental config: fsmonitor.verbose
         if ex.warn and ui.configbool(b'fsmonitor', b'verbose'):
-            if b'illegal_fstypes' not in str(ex):
-                ui.warn(str(ex) + b'\n')
+            if b'illegal_fstypes' not in forcebytestr(ex):
+                ui.warn(forcebytestr(ex) + b'\n')
         if ex.invalidate:
             state.invalidate()
         # experimental config: fsmonitor.verbose