Index: DisjunctionSumScorer.java
===================================================================
--- DisjunctionSumScorer.java	(revision 225378)
+++ DisjunctionSumScorer.java	(working copy)
@@ -167,6 +167,16 @@
         } else {
           currentScore += top.score();
           nrMatchers++;
+          if (nrMatchers > nrScorers) {
+            throw new AssertionError("nrMatchers: " + nrMatchers
+                                     + " bigger than nrScorers: " + nrScorers
+                                     + "\nminimumNrMatchers: " + minimumNrMatchers
+                                     + ", currentDoc: " + currentDoc
+                                     + ", currentScore: " + currentScore
+                                     + "\ntop: " + top
+                                     + "\nscorerQueue.size(): " + scorerQueue.size()
+                                     );
+          }
         }
       } while (true);