diff --git a/src/main/org/apache/tools/ant/Project.java b/src/main/org/apache/tools/ant/Project.java
index d6d2ed1cb..2212b3a09 100644
--- a/src/main/org/apache/tools/ant/Project.java
+++ b/src/main/org/apache/tools/ant/Project.java
@@ -278,6 +278,16 @@ public class Project {
         properties.put(name, value);
     }
 
+    public void unsetProperty(String name) {
+        // command line properties take precedence
+        if (null != userProperties.get(name)) {
+            log("Won\'t unset user property " + name, MSG_VERBOSE);
+            return;
+        }
+        log("Unsetting project property: " + name, MSG_DEBUG);
+        properties.remove(name);
+    }
+
     public void setUserProperty(String name, String value) {
         log("Setting ro project property: " + name + " -> " +
             value, MSG_DEBUG);
diff --git a/src/main/org/apache/tools/ant/taskdefs/Javac.java b/src/main/org/apache/tools/ant/taskdefs/Javac.java
index d258070f3..8f706b6c6 100644
--- a/src/main/org/apache/tools/ant/taskdefs/Javac.java
+++ b/src/main/org/apache/tools/ant/taskdefs/Javac.java
@@ -472,6 +472,7 @@ public class Javac extends MatchingTask {
                    || f.equalsIgnoreCase("false")
                    || f.equalsIgnoreCase("no")) {
             fork = "false";
+            forkedExecutable = null;
         } else {
             fork = "true";
             forkedExecutable = f;
@@ -490,6 +491,11 @@ public class Javac extends MatchingTask {
      * The name of the javac executable to use in fork-mode.
      */
     public String getJavacExecutable() {
+        if (forkedExecutable == null && isForkedJavac()) {
+            forkedExecutable = getSystemJavac();
+        } else if (forkedExecutable != null && !isForkedJavac()) {
+            forkedExecutable = null;
+        }
         return forkedExecutable;
     }
 
diff --git a/src/testcases/org/apache/tools/ant/MockBuildListener.java b/src/testcases/org/apache/tools/ant/MockBuildListener.java
index e71f1c46f..0033794e4 100644
--- a/src/testcases/org/apache/tools/ant/MockBuildListener.java
+++ b/src/testcases/org/apache/tools/ant/MockBuildListener.java
@@ -87,7 +87,7 @@ public class MockBuildListener extends Assert implements BuildListener {
     }
     
     public void assertEmpty() {
-        assertTrue("MockBuilListener is not empty", buffer.isEmpty());
+        assertTrue("MockBuildListener is not empty", buffer.isEmpty());
     }
     
     public void addBuildEvent(final String message, final int priority) {
diff --git a/src/testcases/org/apache/tools/ant/taskdefs/JavacTest.java b/src/testcases/org/apache/tools/ant/taskdefs/JavacTest.java
new file mode 100644
index 000000000..6897d5362
--- /dev/null
+++ b/src/testcases/org/apache/tools/ant/taskdefs/JavacTest.java
@@ -0,0 +1,160 @@
+/*
+ * The Apache Software License, Version 1.1
+ *
+ * Copyright (c) 2001 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", "Ant", 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 Group.
+ *
+ * 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.tools.ant.taskdefs;
+
+import org.apache.tools.ant.Project;
+
+import junit.framework.TestCase;
+
+/**
+ * Testcase for <javac>.
+ *
+ * @author <a href="mailto:stefan.bodewig@epost.de">Stefan Bodewig</a>
+ * @version $Revision$ $Date$
+ */
+public class JavacTest extends TestCase {
+
+    private Project project;
+    private Javac javac;
+
+    public JavacTest(String name) {
+        super(name);
+    }
+
+    public void setUp() {
+        project = new Project();
+        project.init();
+        javac = new Javac();
+        javac.setProject(project);
+    }
+
+    /**
+     * Test setting the name of the javac executable.
+     */
+    public void testForkedExecutableName() {
+        assertNull("no fork means no executable", javac.getJavacExecutable());
+
+        project.setProperty("build.compiler", "modern");
+        assertNull("no fork means no executable", javac.getJavacExecutable());
+
+        javac.setFork("true");
+        assertNotNull("normal fork", javac.getJavacExecutable());
+        assertTrue("name should contain \"javac\"", 
+                   javac.getJavacExecutable().indexOf("javac") > -1);
+
+        project.setProperty("build.compiler", "extJavac");
+        javac.setFork("false");
+        assertNotNull("fork via property", javac.getJavacExecutable());
+        assertTrue("name should contain \"javac\"", 
+                   javac.getJavacExecutable().indexOf("javac") > -1);
+
+        project.setProperty("build.compiler", "whatever");
+        assertNull("no fork and not extJavac means no executable", 
+                   javac.getJavacExecutable());
+
+        String myJavac = "Slartibartfast";
+        javac.setFork(myJavac);
+        assertEquals(myJavac, javac.getJavacExecutable());
+    }
+
+    /**
+     * Test nested compiler args.
+     */
+    public void testCompilerArg() {
+        String[] args = javac.getCurrentCompilerArgs();
+        assertNotNull(args);
+        assertEquals("no args", 0, args.length);
+
+        Javac.ImplementationSpecificArgument arg = javac.createCompilerArg();
+        String ford = "Ford";
+        String prefect = "Prefect";
+        String testArg = ford + " " + prefect;
+        arg.setValue(testArg);
+        args = javac.getCurrentCompilerArgs();
+        assertEquals("unconditional single arg", 1, args.length);
+        assertEquals(testArg, args[0]);
+
+        arg.setImplementation("jikes");
+        args = javac.getCurrentCompilerArgs();
+        assertNotNull(args);
+        assertEquals("implementation is jikes but build.compiler is null", 
+                     0, args.length);
+
+        project.setProperty("build.compiler", "classic");
+        args = javac.getCurrentCompilerArgs();
+        assertNotNull(args);
+        assertEquals("implementation is jikes but build.compiler is classic", 
+                     0, args.length);
+
+        project.setProperty("build.compiler", "jikes");
+        args = javac.getCurrentCompilerArgs();
+        assertEquals("both are jikes", 1, args.length);
+        assertEquals(testArg, args[0]);
+
+        project.unsetProperty("build.compiler");
+        arg.setImplementation("extJavac");
+        javac.setFork("true");
+        args = javac.getCurrentCompilerArgs();
+        assertEquals("both are forked javac", 1, args.length);
+        assertEquals(testArg, args[0]);
+
+        arg.setLine(testArg);
+        args = javac.getCurrentCompilerArgs();
+        assertEquals("split at space", 2, args.length);
+        assertEquals(ford, args[0]);
+        assertEquals(prefect, args[1]);
+    }
+
+}