diff --git lucene/src/test/org/apache/lucene/search/similarities/BasicModelD.java lucene/src/test/org/apache/lucene/search/similarities/BasicModelD.java
index 98594b6..7c253d9 100644
--- lucene/src/test/org/apache/lucene/search/similarities/BasicModelD.java
+++ lucene/src/test/org/apache/lucene/search/similarities/BasicModelD.java
@@ -36,7 +36,8 @@ public class BasicModelD extends BasicModel {
     double nphi = 1 - phi;
     double p = 1.0 / (stats.getNumberOfDocuments() + 1);
     double D = phi * log2(phi / p) + nphi * log2(nphi / (1 - p));
-    return (float)(D * F + 0.5 * log2(2 * Math.PI * tfn * nphi));
+    // nocommit return (float)(D * F + 0.5 * log2(2 * Math.PI * tfn * nphi));
+    return (float)(D * F + 0.5 * log2(1 + 2 * Math.PI * tfn * nphi));
   }
   
   @Override
diff --git lucene/src/test/org/apache/lucene/search/similarities/BasicModelP.java lucene/src/test/org/apache/lucene/search/similarities/BasicModelP.java
index 654133a..72ae4c1 100644
--- lucene/src/test/org/apache/lucene/search/similarities/BasicModelP.java
+++ lucene/src/test/org/apache/lucene/search/similarities/BasicModelP.java
@@ -24,12 +24,19 @@ import static org.apache.lucene.search.similarities.EasySimilarity.log2;
  * @lucene.experimental
  */
 public class BasicModelP extends BasicModel {
+  /** {@code log2(Math.E)}, precomputed. */
+  protected static double LOG2_E = log2(Math.E);
+  
   @Override
   public final float score(EasyStats stats, float tfn) {
     float lambda = (float)stats.getTotalTermFreq() / stats.getNumberOfDocuments();
-    return (float)(tfn * log2(tfn / lambda)
-        + (lambda + 1 / 12 / tfn - tfn) * log2(Math.E)
+//    System.out.printf("tfn=%f, lambda=%f, log1=%f, log2=%f%n", tfn, lambda,
+//        tfn / lambda, 2 * Math.PI * tfn);
+    // nocommit
+    float score = (float)(tfn * log2(tfn / lambda)
+        + (lambda + 1 / 12 / tfn - tfn) * LOG2_E
         + 0.5 * log2(2 * Math.PI * tfn));
+    return score > 0.0f ? score : 0.0f;
   }
 
   @Override
diff --git lucene/src/test/org/apache/lucene/search/similarities/LMDirichletSimilarity.java lucene/src/test/org/apache/lucene/search/similarities/LMDirichletSimilarity.java
index 2c228f8..7db0136 100644
--- lucene/src/test/org/apache/lucene/search/similarities/LMDirichletSimilarity.java
+++ lucene/src/test/org/apache/lucene/search/similarities/LMDirichletSimilarity.java
@@ -25,6 +25,12 @@ import org.apache.lucene.search.Explanation;
  * Ad Hoc information retrieval. In Proceedings of the 24th annual international
  * ACM SIGIR conference on Research and development in information retrieval
  * (SIGIR '01). ACM, New York, NY, USA, 334-342.
+ * <p>
+ * The formula as defined the paper assigns a negative score to documents that
+ * contain the term, but with fewer occurrences than predicted by the collection
+ * language model. The Lucene implementation returns {@code 0} for such
+ * documents.
+ * </p>
  * 
  * @lucene.experimental
  */
@@ -55,10 +61,10 @@ public class LMDirichletSimilarity extends LMSimilarity {
   
   @Override
   protected float score(EasyStats stats, float freq, int docLen) {
-    return stats.getTotalBoost() *
-        (float)(Math.log(1 + freq /
-            (mu * ((LMStats)stats).getCollectionProbability())) +
+    float score = stats.getTotalBoost() * (float)(Math.log(1 + freq /
+        (mu * ((LMStats)stats).getCollectionProbability())) +
         Math.log(mu / (docLen + mu)));
+    return score > 0.0f ? score : 0.0f;
   }
   
   @Override
diff --git lucene/src/test/org/apache/lucene/search/similarities/LMSimilarity.java lucene/src/test/org/apache/lucene/search/similarities/LMSimilarity.java
index 971a4d1..ab8a653 100644
--- lucene/src/test/org/apache/lucene/search/similarities/LMSimilarity.java
+++ lucene/src/test/org/apache/lucene/search/similarities/LMSimilarity.java
@@ -136,12 +136,12 @@ public abstract class LMSimilarity extends EasySimilarity {
   
   /**
    * Models {@code p(w|C)} as the number of occurrences of the term in the
-   * collection, divided by the total number of tokens.
+   * collection, divided by the total number of tokens {@code + 1}.
    */
   public static class DefaultCollectionModel implements CollectionModel {
     @Override
     public float computeProbability(EasyStats stats) {
-      return (float)stats.getTotalTermFreq() / stats.getNumberOfFieldTokens();
+      return (float)stats.getTotalTermFreq() / (stats.getNumberOfFieldTokens() +1);
     }
     
     @Override
diff --git lucene/src/test/org/apache/lucene/search/similarities/TestEasySimilarity.java lucene/src/test/org/apache/lucene/search/similarities/TestEasySimilarity.java
index ad7799b..fd2bf10 100644
--- lucene/src/test/org/apache/lucene/search/similarities/TestEasySimilarity.java
+++ lucene/src/test/org/apache/lucene/search/similarities/TestEasySimilarity.java
@@ -459,4 +459,4 @@ public class TestEasySimilarity extends LuceneTestCase {
       return sim;
     }
   }
-}
\ No newline at end of file
+}