diff --git a/src/java/org/apache/commons/math/special/Gamma.java b/src/java/org/apache/commons/math/special/Gamma.java
index dbd98f388..87b1b2612 100644
--- a/src/java/org/apache/commons/math/special/Gamma.java
+++ b/src/java/org/apache/commons/math/special/Gamma.java
@@ -113,10 +113,10 @@ public class Gamma {
     public static double regularizedGammaP(double a, double x, double epsilon, int maxIterations) {
         double ret;
 
-        if (a <= 0.0) {
-            throw new IllegalArgumentException("a must be positive");
-        } else if (x <= 0.0) {
-            throw new IllegalArgumentException("x must be non-negative");
+        if (Double.isNaN(a) || Double.isNaN(x) || (a <= 0.0) || (x < 0.0)) {
+            ret = Double.NaN;
+        } else if (x == 0.0) {
+            ret = 0.0;
         } else {
             // calculate series
             double n = 0.0; // current element index
@@ -165,9 +165,8 @@ public class Gamma {
     public static double logGamma(double x, double epsilon, int maxIterations) {
         double ret;
 
-        if (x <= 0.0) {
-            throw new IllegalArgumentException(
-                "x must be non-negative");
+        if (Double.isNaN(x) || (x <= 0.0)) {
+            ret = Double.NaN;
         } else {
             double g = 607.0 / 128.0;
 
@@ -205,3 +204,4 @@ public class Gamma {
         return ret;
     }
 }
+
diff --git a/src/test/org/apache/commons/math/special/GammaTest.java b/src/test/org/apache/commons/math/special/GammaTest.java
new file mode 100644
index 000000000..09e54138b
--- /dev/null
+++ b/src/test/org/apache/commons/math/special/GammaTest.java
@@ -0,0 +1,125 @@
+/* ====================================================================
+ * The Apache Software License, Version 1.1
+ *
+ * Copyright (c) 2003 The Apache Software Foundation.  All rights
+ * reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * 3. The end-user documentation included with the redistribution, if
+ *    any, must include the following acknowlegement:
+ *       "This product includes software developed by the
+ *        Apache Software Foundation (http://www.apache.org/)."
+ *    Alternately, this acknowlegement may appear in the software itself,
+ *    if and wherever such third-party acknowlegements normally appear.
+ *
+ * 4. The names "The Jakarta Project", "Commons", and "Apache Software
+ *    Foundation" must not be used to endorse or promote products derived
+ *    from this software without prior written permission. For written
+ *    permission, please contact apache@apache.org.
+ *
+ * 5. Products derived from this software may not be called "Apache"
+ *    nor may "Apache" appear in their names without prior written
+ *    permission of the Apache Software Foundation.
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
+ * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+ * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ */
+package org.apache.commons.math.special;
+
+import org.apache.commons.math.TestUtils;
+
+import junit.framework.TestCase;
+
+/**
+ * @author Brent Worden
+ */
+public class GammaTest extends TestCase {
+    /**
+     * Constructor for BetaTest.
+     * @param name
+     */
+    public GammaTest(String name) {
+        super(name);
+    }
+
+    private void testRegularizedGamma(double expected, double a, double x) {
+        double actual = Gamma.regularizedGammaP(a, x);
+        TestUtils.assertEquals(expected, actual, 10e-5);
+    }
+
+    private void testLogGamma(double expected, double x) {
+        double actual = Gamma.logGamma(x, 10e-5, Integer.MAX_VALUE);
+        TestUtils.assertEquals(expected, actual, 10e-5);
+    }
+
+    public void testRegularizedGammaNanPositive() {
+        testRegularizedGamma(Double.NaN, Double.NaN, 1.0);
+    }
+
+    public void testRegularizedGammaPositiveNan() {
+        testRegularizedGamma(Double.NaN, 1.0, Double.NaN);
+    }
+    
+    public void testRegularizedGammaNegativePositive() {
+        testRegularizedGamma(Double.NaN, -1.5, 1.0);
+    }
+    
+    public void testRegularizedGammaPositiveNegative() {
+        testRegularizedGamma(Double.NaN, 1.0, -1.0);
+    }
+    
+    public void testRegularizedGammaZeroPositive() {
+        testRegularizedGamma(Double.NaN, 0.0, 1.0);
+    }
+    
+    public void testRegularizedGammaPositiveZero() {
+        testRegularizedGamma(0.0, 1.0, 0.0);
+    }
+    
+    public void testRegularizedGammaPositivePositive() {
+        testRegularizedGamma(0.632121, 1.0, 1.0);
+    }
+    
+    public void testLogGammaNan() {
+        testLogGamma(Double.NaN, Double.NaN);
+    }
+    
+    public void testLogGammaNegative() {
+        testLogGamma(Double.NaN, -1.0);
+    }
+    
+    public void testLogGammaZero() {
+        testLogGamma(Double.NaN, 0.0);
+    }
+    
+    public void testLogGammaPositive() {
+        testLogGamma(0.693147, 3.0);
+    }
+}