diff --git a/parso/python/normalizer.py b/parso/python/normalizer.py
index d4c9710..02b83a9 100644
--- a/parso/python/normalizer.py
+++ b/parso/python/normalizer.py
@@ -204,6 +204,13 @@ class ErrorFinder(Normalizer):
                 self._add_indentation_error(message, spacing)
             else:
                 self._add_syntax_error('invalid syntax', leaf)
+        elif leaf.type == 'string':
+            if 'b' in leaf.string_prefix.lower() \
+                    and any(c for c in leaf.value if ord(c) > 127):
+                # TODO add check for python 3
+                # b'ä'
+                message = "bytes can only contain ASCII literal characters."
+                self._add_syntax_error(message, leaf)
         elif leaf.value == 'continue':
             in_loop = False
             for block in self._context.blocks:
diff --git a/test/test_python_errors.py b/test/test_python_errors.py
index 478deea..818a41e 100644
--- a/test/test_python_errors.py
+++ b/test/test_python_errors.py
@@ -120,6 +120,7 @@ def test_python_exception_matches(code):
         ('[*[] for a in [1]]', '3.5'),
         ('{**{} for a in [1]}', '3.5'),
         ('"s" b""', '3.5'),
+        ('b"ä"', '3.5'),
     ]
 )
 def test_python_exception_matches_version(code, version):