diff -r a644c5b44d09 lucene/src/java/org/apache/lucene/search/BooleanQuery.java
--- a/lucene/src/java/org/apache/lucene/search/BooleanQuery.java	Tue Sep 07 16:04:54 2010 +0000
+++ b/lucene/src/java/org/apache/lucene/search/BooleanQuery.java	Wed Sep 08 06:29:09 2010 -0400
@@ -240,6 +240,11 @@
         Weight w = wIter.next();
         BooleanClause c = cIter.next();
         if (w.scorer(reader, true, true) == null) {
+          if (c.isRequired()) {
+            fail = true;
+            Explanation r = new Explanation(0.0f, "no match on required clause (" + c.getQuery().toString() + ")");
+            sumExpl.addDetail(r);
+          }
           continue;
         }
         Explanation e = w.explain(reader, doc);