diff --git a/tests/heredoctest.py b/tests/heredoctest.py
new file mode 100644
--- /dev/null
+++ b/tests/heredoctest.py
@@ -0,0 +1,9 @@
+import doctest, tempfile, os, sys
+
+if __name__ == "__main__":
+    fd, name = tempfile.mkstemp(suffix='hg-tst')
+    os.write(fd, sys.stdin.read())
+    os.close(fd)
+    failures, _ = doctest.testfile(name, module_relative=False)
+    if failures:
+        sys.exit(1)