Index: Lib/test/test_struct.py
===================================================================
--- Lib/test/test_struct.py	(revision 81890)
+++ Lib/test/test_struct.py	(working copy)
@@ -443,7 +443,7 @@
 
         # Test bogus offset (issue 3694)
         sb = small_buf
-        self.assertRaises(TypeError, struct.pack_into, b'1', sb, None)
+        self.assertRaises(TypeError, struct.pack_into, b'l', sb, None)
 
     def test_pack_into_fn(self):
         test_string = b'Reykjavik rocks, eow!'
@@ -510,7 +510,33 @@
         def test_crasher(self):
             self.assertRaises(MemoryError, struct.pack, "357913941b", "a")
 
+    def test_trailing_counter(self):
+        store = array.array('b', b' '*100)
+ 
+        # format lists containing only count spec should result in an error
+        self.assertRaises(struct.error, struct.pack, '12345')
+        self.assertRaises(struct.error, struct.unpack, '12345', '')
+        self.assertRaises(struct.error, struct.pack_into, '12345', store, 0)
+        self.assertRaises(struct.error, struct.unpack_from, '12345', store, 0)
 
+        # Format lists with trailing count spec should result in an error
+        self.assertRaises(struct.error, struct.pack, 'c12345', 'x')
+        self.assertRaises(struct.error, struct.unpack, 'c12345', 'x')
+        self.assertRaises(struct.error, struct.pack_into, 'c12345', store, 0,
+                           'x')
+        self.assertRaises(struct.error, struct.unpack_from, 'c12345', store, 
+                           0)
+ 
+        # Mixed format tests
+        self.assertRaises(struct.error, struct.pack, '14s42', 'spam and eggs')
+        self.assertRaises(struct.error, struct.unpack, '14s42', 
+                          'spam and eggs')
+        self.assertRaises(struct.error, struct.pack_into, '14s42', store, 0,
+                          'spam and eggs')
+        self.assertRaises(struct.error, struct.unpack_from, '14s42', store, 0)
+ 
+
+
 def test_main():
     run_unittest(StructTest)
 
Index: Modules/_struct.c
===================================================================
--- Modules/_struct.c	(revision 81890)
+++ Modules/_struct.c	(working copy)
@@ -1195,8 +1195,11 @@
                 }
                 num = x;
             }
-            if (c == '\0')
-                break;
+            if (c == '\0') {
+                PyErr_SetString(StructError,
+                                "repeat count given without format specifier");
+                return -1;
+            }
         }
         else
             num = 1;