diff --git a/Lib/_strptime.py b/Lib/_strptime.py
index 81c105f..4b7a7dd 100644
--- a/Lib/_strptime.py
+++ b/Lib/_strptime.py
@@ -423,6 +423,9 @@
     found = format_regex.match(data_string)
     if not found:
         raise ValueError("time data did not match format")
+    if len(data_string) != found.end():
+        raise ValueError("unconverted data remains: %s" %
+                          data_string[found.end():])
     year = 1900
     month = day = 1
     hour = minute = second = 0
diff --git a/Lib/test/test_strptime.py b/Lib/test/test_strptime.py
index a106a42..2c3955b 100644
--- a/Lib/test/test_strptime.py
+++ b/Lib/test/test_strptime.py
@@ -227,6 +227,10 @@
         self.assertRaises(ValueError, _strptime.strptime, data_string="%d",
                           format="%A")
 
+    def test_unconverteddata(self):
+        # Check ValueError is raised when there is unconverted data
+        self.assertRaises(ValueError, _strptime.strptime, "10 12", "%m")
+
     def helper(self, directive, position):
         """Helper fxn in testing."""
         strf_output = time.strftime("%" + directive, self.time_tuple)