diff --git a/src/java/org/apache/commons/math/distribution/BinomialDistributionImpl.java b/src/java/org/apache/commons/math/distribution/BinomialDistributionImpl.java
index 382eaf38b..a29a13a0c 100644
--- a/src/java/org/apache/commons/math/distribution/BinomialDistributionImpl.java
+++ b/src/java/org/apache/commons/math/distribution/BinomialDistributionImpl.java
@@ -24,7 +24,7 @@ import org.apache.commons.math.util.MathUtils;
 /**
  * The default implementation of {@link BinomialDistribution}.
  *
- * @version $Revision: 1.17 $ $Date: 2004/07/23 05:22:36 $
+ * @version $Revision: 1.18 $ $Date: 2004/07/25 16:29:24 $
  */
 public class BinomialDistributionImpl
     extends AbstractDiscreteDistribution
@@ -162,6 +162,9 @@ public class BinomialDistributionImpl
     /**
      * For this distribution, X, this method returns the largest x, such
      * that P(X &le; x) &le; <code>p</code>.
+     * <p>
+     * Returns <code>-1</code> for p=0 and <code>Integer.MAX_VALUE</code> for
+     * p=1.
      *
      * @param p the desired probability
      * @return the largest x such that P(X &le; x) <= p
@@ -172,7 +175,7 @@ public class BinomialDistributionImpl
     public int inverseCumulativeProbability(final double p) throws MathException {
         // handle extreme values explicitly
         if (p == 0) {
-            return 0;
+            return -1;
         } 
         if (p == 1) {
             return Integer.MAX_VALUE; 
diff --git a/src/java/org/apache/commons/math/distribution/DiscreteDistribution.java b/src/java/org/apache/commons/math/distribution/DiscreteDistribution.java
index 8fb089390..c117a933d 100644
--- a/src/java/org/apache/commons/math/distribution/DiscreteDistribution.java
+++ b/src/java/org/apache/commons/math/distribution/DiscreteDistribution.java
@@ -20,7 +20,7 @@ import org.apache.commons.math.MathException;
 /**
  * Base interface for various discrete distributions.
  *
- * @version $Revision: 1.15 $ $Date: 2004/06/23 16:26:15 $
+ * @version $Revision: 1.16 $ $Date: 2004/07/25 16:29:24 $
  */
 public interface DiscreteDistribution {
     /**
@@ -51,11 +51,26 @@ public interface DiscreteDistribution {
     double cumulativeProbability(int x0, int x1) throws MathException;
     
     /**
-     * For this distribution, X, this method returns the largest x such that P(X &le; x) <= p.
+     * For this distribution, X, this method returns the largest x such that
+     * P(X &le; x) <= p.
+     * <p>
+     * Note that this definition implies: <ul>
+     * <li> If there is a minimum value, <code>m</code>, with postive
+     * probablility under (the density of) X, then <code>m - 1</code> is
+     * returned by <code>inverseCumulativeProbability(0).</code>  If there is
+     * no such value <code>m,  Integer.MIN_VALUE</code> is 
+     * returned.</li>
+     * <li> If there is a maximum value, <code>M</code>, such that
+     * P(X &le; M) =1, then <code>M</code> is returned by 
+     * <code>inverseCumulativeProbability(1).</code>
+     * If there is no such value, <code>M, Integer.MAX_VALUE</code> is 
+     * returned.</li></ul>
+     * 
      * @param p the cumulative probability.
-     * @return x. 
+     * @return the largest x such that P(X &le; x) <= p
      * @throws MathException if the inverse cumulative probability can not be
      *            computed due to convergence or other numerical errors.
+     * @throws IllegalArgumentException if p is not between 0 and 1 (inclusive)
      */
     int inverseCumulativeProbability(double p) throws MathException;
 }
diff --git a/src/test/org/apache/commons/math/distribution/BinomialDistributionTest.java b/src/test/org/apache/commons/math/distribution/BinomialDistributionTest.java
index 56b1650de..666796a41 100644
--- a/src/test/org/apache/commons/math/distribution/BinomialDistributionTest.java
+++ b/src/test/org/apache/commons/math/distribution/BinomialDistributionTest.java
@@ -20,7 +20,7 @@ package org.apache.commons.math.distribution;
  * Extends DiscreteDistributionAbstractTest.  See class javadoc for
  * DiscreteDistributionAbstractTest for details.
  * 
- * @version $Revision: 1.14 $ $Date: 2004/07/23 05:22:36 $
+ * @version $Revision: 1.15 $ $Date: 2004/07/25 16:29:25 $
  */
 public class BinomialDistributionTest extends DiscreteDistributionAbstractTest {
     
@@ -69,7 +69,7 @@ public class BinomialDistributionTest extends DiscreteDistributionAbstractTest {
     
     /** Creates the default inverse cumulative probability density test expected values */
     public int[] makeInverseCumulativeTestValues() {
-        return new int[] {0,1, 2, 3, 4, 4, 9, 9, 9, 8, 8, Integer.MAX_VALUE};
+        return new int[] {-1, 1, 2, 3, 4, 4, 9, 9, 9, 8, 8, Integer.MAX_VALUE};
     }
 
     //----------------- Additional test cases ---------------------------------
diff --git a/src/test/org/apache/commons/math/distribution/HypergeometricDistributionTest.java b/src/test/org/apache/commons/math/distribution/HypergeometricDistributionTest.java
index 8682435c9..19aaf676d 100644
--- a/src/test/org/apache/commons/math/distribution/HypergeometricDistributionTest.java
+++ b/src/test/org/apache/commons/math/distribution/HypergeometricDistributionTest.java
@@ -21,7 +21,7 @@ package org.apache.commons.math.distribution;
  * Extends DiscreteDistributionAbstractTest.  See class javadoc for
  * DiscreteDistributionAbstractTest for details.
  * 
- * @version $Revision: 1.11 $ $Date: 2004/05/11 02:12:11 $
+ * @version $Revision: 1.12 $ $Date: 2004/07/25 16:29:25 $
  */
 public class HypergeometricDistributionTest extends DiscreteDistributionAbstractTest {
 
@@ -64,13 +64,13 @@ public class HypergeometricDistributionTest extends DiscreteDistributionAbstract
     
     /** Creates the default inverse cumulative probability test input values */
     public double[] makeInverseCumulativeTestPoints() {
-        return new double[] {0.001d, 0.010d, 0.025d, 0.050d, 0.100d, 0.999d,
-                0.990d, 0.975d, 0.950d, 0.900d}; 
+        return new double[] {0d, 0.001d, 0.010d, 0.025d, 0.050d, 0.100d, 0.999d,
+                0.990d, 0.975d, 0.950d, 0.900d, 1d}; 
     }
     
     /** Creates the default inverse cumulative probability density test expected values */
     public int[] makeInverseCumulativeTestValues() {
-        return new int[] {-1, 0, 0, 0, 0, 4, 3, 3, 3, 3};
+        return new int[] {-1, -1, 0, 0, 0, 0, 4, 3, 3, 3, 3, 5};
     }
     
     //-------------------- Additional test cases ------------------------------