Index: Lib/test/test_normalization.py
===================================================================
--- Lib/test/test_normalization.py	(revision 87322)
+++ Lib/test/test_normalization.py	(working copy)
@@ -54,9 +54,6 @@
             if line.startswith("@Part"):
                 part = line.split()[0]
                 continue
-            if part == "@Part3":
-                # XXX we don't support PRI #29 yet, so skip these tests for now
-                continue
             try:
                 c1,c2,c3,c4,c5 = [unistr(x) for x in line.split(';')[:-1]]
             except RangeError:
Index: Modules/unicodedata.c
===================================================================
--- Modules/unicodedata.c	(revision 87322)
+++ Modules/unicodedata.c	(working copy)
@@ -684,10 +684,14 @@
       comb = 0;
       while (i1 < end) {
           int comb1 = _getrecord_ex(*i1)->combining;
-          if (comb && (comb1 == 0 || comb == comb1)) {
-              /* Character is blocked. */
-              i1++;
-              continue;
+          if (comb) {
+              if (comb1 == 0)
+                  break;
+              if (comb == comb1) {
+                  /* Character is blocked. */
+                  i1++;
+                  continue;
+              }
           }
           l = find_nfc_index(self, nfc_last, *i1);
           /* *i1 cannot be combined with *i. If *i1
@@ -711,6 +715,7 @@
           /* Replace the original character. */
           *i = code;
           /* Mark the second character unused. */
+          assert(cskipped < 20);
           skipped[cskipped++] = i1;
           i1++;
           f = find_nfc_index(self, nfc_first, *i);