Index: CHANGES.txt
===================================================================
--- CHANGES.txt	(revision 912360)
+++ CHANGES.txt	(working copy)
@@ -603,10 +603,10 @@
     code to implement this method.  If you already extend
     IndexSearcher, no further changes are needed to use Collector.
     
-    Finally, the values Float.NaN, Float.NEGATIVE_INFINITY and
-    Float.POSITIVE_INFINITY are not valid scores.  Lucene uses these
-    values internally in certain places, so if you have hits with such
-    scores, it will cause problems. (Shai Erera via Mike McCandless)
+    Finally, the values Float.NaN and Float.NEGATIVE_INFINITY are not
+    valid scores.  Lucene uses these values internally in certain
+    places, so if you have hits with such scores, it will cause
+    problems. (Shai Erera via Mike McCandless)
 
  * LUCENE-1687: All methods and parsers from the interface ExtendedFieldCache
     have been moved into FieldCache. ExtendedFieldCache is now deprecated and
@@ -684,7 +684,7 @@
     
  * LUCENE-1575: As of 2.9, the core collectors as well as
     IndexSearcher's search methods that return top N results, no
-    longer filter out zero scoring documents. If you rely on this
+    longer filter documents with scores <= 0.0. If you rely on this
     functionality you can use PositiveScoresOnlyCollector like this:
 
     <code>
Index: src/java/org/apache/lucene/search/TopScoreDocCollector.java
===================================================================
--- src/java/org/apache/lucene/search/TopScoreDocCollector.java	(revision 912360)
+++ src/java/org/apache/lucene/search/TopScoreDocCollector.java	(working copy)
@@ -29,10 +29,10 @@
  * instance of this collector you should know in advance whether documents are
  * going to be collected in doc Id order or not.
  *
- * <p><b>NOTE</b>: The values Float.Nan,
- * Float.NEGATIVE_INFINITY and Float.POSITIVE_INFINITY are
- * not valid scores.  This collector will not properly
- * collect hits with such scores.
+ * <p><b>NOTE</b>: The values Float.Nan and
+ * Float.NEGATIVE_INFINITY are not valid scores.  This
+ * collector will not properly collect hits with such
+ * scores.
  */
 public abstract class TopScoreDocCollector extends TopDocsCollector<ScoreDoc> {
 
@@ -45,6 +45,11 @@
     @Override
     public void collect(int doc) throws IOException {
       float score = scorer.score();
+
+      // This collector cannot handle these scores:
+      assert score != Float.NEGATIVE_INFINITY;
+      assert score != Float.NaN;
+
       totalHits++;
       if (score <= pqTop.score) {
         // Since docs are returned in-order (i.e., increasing doc Id), a document
@@ -72,6 +77,10 @@
     @Override
     public void collect(int doc) throws IOException {
       float score = scorer.score();
+
+      // This collector cannot handle NaN
+      assert score != Float.NaN;
+
       totalHits++;
       doc += docBase;
       if (score < pqTop.score || (score == pqTop.score && doc > pqTop.doc)) {