diff --git a/hgext/fastannotate/context.py b/hgext/fastannotate/context.py
--- a/hgext/fastannotate/context.py
+++ b/hgext/fastannotate/context.py
@@ -602,7 +602,7 @@
         the best case, the user provides a node and we don't need to read the
         filelog or construct any filecontext.
         """
-        if isinstance(f, str):
+        if isinstance(f, bytes):
             hsh = f
         else:
             hsh = f.node()
@@ -625,7 +625,7 @@
         if showpath:
             result = self._addpathtoresult(result)
         if showlines:
-            if isinstance(f, str): # f: node or fctx
+            if isinstance(f, bytes): # f: node or fctx
                 llrev = self.revmap.hsh2rev(f)
                 fctx = self._resolvefctx(f, self.revmap.rev2path(llrev))
             else: