diff --git a/.travis.yml b/.travis.yml
index ae08482d..e51b2e0c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -12,5 +12,10 @@ matrix:
       dist: xenial
     - python: nightly
       dist: xenial
+# TODO: https://bugs.python.org/issue40334
+# the PEG parser is currently broken in some cases
+  allow_failures:
+    - python: nightly
+      dist: xenial
 install: pip install tox
 script: tox -e py
diff --git a/pyflakes/test/test_api.py b/pyflakes/test/test_api.py
index 128aa69d..b579ac8e 100644
--- a/pyflakes/test/test_api.py
+++ b/pyflakes/test/test_api.py
@@ -449,6 +449,8 @@ def evaluate(source):
         with self.makeTempFile(source) as sourcePath:
             if PYPY:
                 message = 'end of file (EOF) while scanning triple-quoted string literal'
+            elif sys.version_info >= (3, 9):
+                message = 'invalid string prefix'
             else:
                 message = 'invalid syntax'