Index: Lib/test/test_struct.py
===================================================================
--- Lib/test/test_struct.py	(revision 64324)
+++ Lib/test/test_struct.py	(working copy)
@@ -573,8 +573,33 @@
         def test_crasher(self):
             self.assertRaises(MemoryError, struct.pack, "357913941c", "a")
 
+    def test_trailing_counter(self):
+        store = array.array('c', ' '*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 64324)
+++ Modules/_struct.c	(working copy)
@@ -1357,8 +1357,11 @@
 				}
 				num = x;
 			}
-			if (c == '\0')
-				break;
+			if (c == '\0') {
+				PyErr_SetString(StructError,
+						"repeat count given without format specifier");
+				return -1;
+			}
 		}
 		else
 			num = 1;