diff -r b07488490001 Lib/test/test_codecs.py
--- a/Lib/test/test_codecs.py	Fri Apr 20 14:36:47 2012 +0200
+++ b/Lib/test/test_codecs.py	Wed Apr 25 20:08:37 2012 +0300
@@ -540,8 +540,19 @@
         )
 
     def test_errors(self):
-        self.assertRaises(UnicodeDecodeError, codecs.utf_16_le_decode,
-                          b"\xff", "strict", True)
+        tests = [
+            (b'\xff', '\ufffd'),
+            (b'A\x00Z', 'A\ufffd'),
+            (b'A\x00B\x00C\x00D\x00Z', 'ABCD\ufffd'),
+            (b'\x00\xd8', '\ufffd'),
+            (b'\x00\xd8A', '\ufffd'),
+            (b'\x00\xd8A\x00', '\ufffdA'),
+            (b'\x00\xdcA\x00', '\ufffdA'),
+        ]
+        for raw, expected in tests:
+            self.assertRaises(UnicodeDecodeError, codecs.utf_16_le_decode,
+                              raw, 'strict', True)
+            self.assertEqual(raw.decode('utf-16le', 'replace'), expected)
 
     def test_nonbmp(self):
         self.assertEqual("\U00010203".encode(self.encoding),
@@ -568,8 +579,19 @@
         )
 
     def test_errors(self):
-        self.assertRaises(UnicodeDecodeError, codecs.utf_16_be_decode,
-                          b"\xff", "strict", True)
+        tests = [
+            (b'\xff', '\ufffd'),
+            (b'\x00A\xff', 'A\ufffd'),
+            (b'\x00A\x00B\x00C\x00DZ', 'ABCD\ufffd'),
+            (b'\xd8\x00', '\ufffd'),
+            (b'\xd8\x00\xdc', '\ufffd'),
+            (b'\xd8\x00\x00A', '\ufffdA'),
+            (b'\xdc\x00\x00A', '\ufffdA'),
+        ]
+        for raw, expected in tests:
+            self.assertRaises(UnicodeDecodeError, codecs.utf_16_be_decode,
+                              raw, 'strict', True)
+            self.assertEqual(raw.decode('utf-16be', 'replace'), expected)
 
     def test_nonbmp(self):
         self.assertEqual("\U00010203".encode(self.encoding),
diff -r b07488490001 Objects/unicodeobject.c
--- a/Objects/unicodeobject.c	Fri Apr 20 14:36:47 2012 +0200
+++ b/Objects/unicodeobject.c	Wed Apr 25 20:08:37 2012 +0300
@@ -3425,7 +3425,7 @@
     /* Unpack UTF-16 encoded data */
     p = unicode->str;
     q = (unsigned char *)s;
-    e = q + size - 1;
+    e = q + size;
 
     if (byteorder)
         bo = *byteorder;
@@ -3476,8 +3476,20 @@
 #endif
 
     aligned_end = (const unsigned char *) ((size_t) e & ~LONG_PTR_MASK);
-    while (q < e) {
+    while (1) {
         Py_UNICODE ch;
+        if (e - q < 2) {
+            /* remaining byte at the end? (size should be even) */
+            if (q == e || consumed)
+                break;
+            errmsg = "truncated data";
+            startinpos = ((const char *)q) - starts;
+            endinpos = ((const char *)e) - starts;
+            outpos = p - PyUnicode_AS_UNICODE(unicode);
+            goto utf16Error;
+            /* The remaining input chars are ignored if the callback
+               chooses to skip the input */
+        }
         /* First check for possible aligned read of a C 'long'. Unaligned
            reads are more expensive, better to defer to another iteration. */
         if (!((size_t) q & LONG_PTR_MASK)) {
@@ -3546,8 +3558,8 @@
             }
             p = _p;
             q = _q;
-            if (q >= e)
-                break;
+            if (e - q < 2)
+                continue;
         }
         ch = (q[ihi] << 8) | q[ilo];
 
@@ -3559,10 +3571,10 @@
         }
 
         /* UTF-16 code pair: */
-        if (q > e) {
+        if (e - q < 2) {
             errmsg = "unexpected end of data";
             startinpos = (((const char *)q) - 2) - starts;
-            endinpos = ((const char *)e) + 1 - starts;
+            endinpos = ((const char *)e) - starts;
             goto utf16Error;
         }
         if (0xD800 <= ch && ch <= 0xDBFF) {
@@ -3606,31 +3618,9 @@
                 &outpos,
                 &p))
             goto onError;
-    }
-    /* remaining byte at the end? (size should be even) */
-    if (e == q) {
-        if (!consumed) {
-            errmsg = "truncated data";
-            startinpos = ((const char *)q) - starts;
-            endinpos = ((const char *)e) + 1 - starts;
-            outpos = p - PyUnicode_AS_UNICODE(unicode);
-            if (unicode_decode_call_errorhandler(
-                    errors,
-                    &errorHandler,
-                    "utf16", errmsg,
-                    &starts,
-                    (const char **)&e,
-                    &startinpos,
-                    &endinpos,
-                    &exc,
-                    (const char **)&q,
-                    &unicode,
-                    &outpos,
-                    &p))
-                goto onError;
-            /* The remaining input chars are ignored if the callback
-               chooses to skip the input */
-        }
+        /* Update data because unicode_decode_call_errorhandler might have
+           changed the input object. */
+        aligned_end = (const unsigned char *) ((size_t) e & ~LONG_PTR_MASK);
     }
 
     if (byteorder)