diff --git a/docs/manual/CoreTypes/mapper.html b/docs/manual/CoreTypes/mapper.html
index 914c1ea1c..365620930 100644
--- a/docs/manual/CoreTypes/mapper.html
+++ b/docs/manual/CoreTypes/mapper.html
@@ -221,7 +221,7 @@ leading directory information stripped off. Both <code>to</code> and
     <!--                                        -->
 
 <h4><a name="glob-mapper">glob</a></h4>
-<p>Both <code>to</code> and <code>from</code> define patterns that may
+<p>Both <code>to</code> and <code>from</code> are required and define patterns that may
 contain at most one <code>*</code>. For each source file that matches
 the <code>from</code> pattern, a target file name will be constructed
 from the <code>to</code> pattern by substituting the <code>*</code> in
@@ -350,7 +350,7 @@ that don't match the <code>from</code> pattern will be ignored.</p>
     <!--                                        -->
 
 <h4><a name="regexp-mapper">regexp</a></h4>
-<p>Both <code>to</code> and <code>from</code> define regular
+<p>Both <code>to</code> and <code>from</code> are required and define regular
 expressions. If the source file name matches the <code>from</code>
 pattern, the target file name will be constructed from the
 <code>to</code> pattern, using <code>\0</code> to <code>\9</code> as
@@ -571,6 +571,7 @@ the package mapper replaces
 directory separators found in the matched source pattern with dots in the target
 pattern placeholder. This mapper is particularly useful in combination
 with <code>&lt;uptodate&gt;</code> and <code>&lt;junit&gt;</code> output.</p>
+<p>The to and from attributes are both required.</p>
 <b>Example:</b>
 <blockquote><pre>
 &lt;mapper type="package" from="*Test.java" to="TEST-*Test.xml"/&gt;
@@ -602,6 +603,7 @@ with <code>&lt;uptodate&gt;</code> and <code>&lt;junit&gt;</code> output.</p>
     test cases. The mapper shares the sample syntax
     as the <a href="#glob-mapper">glob mapper</a>.
   </p>
+<p>The to and from attributes are both required.</p>
 <b>Example:</b>
 <blockquote><pre>
 &lt;mapper type="unpackage" from="TEST-*Test.xml" to="${test.src.dir}/*Test.java"&gt;
diff --git a/src/main/org/apache/tools/ant/util/GlobPatternMapper.java b/src/main/org/apache/tools/ant/util/GlobPatternMapper.java
index 24f4fede4..9aabf969b 100644
--- a/src/main/org/apache/tools/ant/util/GlobPatternMapper.java
+++ b/src/main/org/apache/tools/ant/util/GlobPatternMapper.java
@@ -18,6 +18,8 @@
 
 package org.apache.tools.ant.util;
 
+import org.apache.tools.ant.BuildException;
+
 /**
  * Implementation of FileNameMapper that does simple wildcard pattern
  * replacements.
@@ -95,6 +97,7 @@ public class GlobPatternMapper implements FileNameMapper {
      * @param from a string
      */
     public void setFrom(String from) {
+        if (from != null) {
         int index = from.lastIndexOf("*");
         if (index == -1) {
             fromPrefix = from;
@@ -105,6 +108,9 @@ public class GlobPatternMapper implements FileNameMapper {
         }
         prefixLength = fromPrefix.length();
         postfixLength = fromPostfix.length();
+        } else {
+            throw new BuildException("this mapper requires a 'from' attribute");
+        }
     }
 
     /**
@@ -112,6 +118,7 @@ public class GlobPatternMapper implements FileNameMapper {
      * @param to a string
      */
     public void setTo(String to) {
+        if (to != null) {
         int index = to.lastIndexOf("*");
         if (index == -1) {
             toPrefix = to;
@@ -120,6 +127,9 @@ public class GlobPatternMapper implements FileNameMapper {
             toPrefix = to.substring(0, index);
             toPostfix = to.substring(index + 1);
         }
+        } else {
+            throw new BuildException("this mapper requires a 'to' attribute");
+        }
     }
 
     /**
diff --git a/src/main/org/apache/tools/ant/util/RegexpPatternMapper.java b/src/main/org/apache/tools/ant/util/RegexpPatternMapper.java
index 51ad6e652..2971daaed 100644
--- a/src/main/org/apache/tools/ant/util/RegexpPatternMapper.java
+++ b/src/main/org/apache/tools/ant/util/RegexpPatternMapper.java
@@ -80,6 +80,7 @@ public class RegexpPatternMapper implements FileNameMapper {
      * @throws BuildException on error.
      */
     public void setFrom(String from) throws BuildException {
+        if (from != null) {
         try {
             reg.setPattern(from);
         } catch (NoClassDefFoundError e) {
@@ -88,6 +89,9 @@ public class RegexpPatternMapper implements FileNameMapper {
             throw new BuildException("Cannot load regular expression matcher",
                                      e);
         }
+        } else {
+            throw new BuildException("this mapper requires a 'from' attribute");
+        }
     }
 
     /**
@@ -96,7 +100,11 @@ public class RegexpPatternMapper implements FileNameMapper {
      * @throws BuildException on error.
      */
     public void setTo(String to) {
+        if (to != null) {
         this.to = to.toCharArray();
+        } else {
+            throw new BuildException("this mapper requires a 'to' attribute");
+        }
     }
 
     /**