diff --git a/vmprof/reader.py b/vmprof/reader.py
index 34a1857b..cf527d33 100644
--- a/vmprof/reader.py
+++ b/vmprof/reader.py
@@ -163,7 +163,7 @@ def read_header(self):
 
         lgt = ord(fileobj.read(1))
         s.interp_name = fileobj.read(lgt)
-        if s.interp_name == 'pypy':
+        if s.interp_name == b'pypy':
             s.profile_rpython = True
         if PY3:
             s.interp_name = s.interp_name.decode()