Index: src/main/java/org/apache/maven/shared/invoker/MavenCommandLineBuilder.java
===================================================================
--- src/main/java/org/apache/maven/shared/invoker/MavenCommandLineBuilder.java	(revision 898681)
+++ src/main/java/org/apache/maven/shared/invoker/MavenCommandLineBuilder.java	(working copy)
@@ -232,8 +232,10 @@
                 String key = (String) entry.getKey();
                 String value = (String) entry.getValue();
 
-                cli.createArg().setValue( "-D" );
-                cli.createArg().setValue( key + '=' + value );
+                if (value == null || value.length()==0)
+                	cli.createArg().setValue( "-D" + key );
+                else
+                	cli.createArg().setValue( "-D" + key + '=' + value );
             }
         }
     }
@@ -445,7 +447,7 @@
         {
             cli.createArg().setValue( "-npu" );
         }
-        
+
         if ( request.isShowVersion() )
         {
             cli.createArg().setValue( "-V" );
@@ -518,7 +520,7 @@
 
     /**
      * Wraps a path with quotes to handle paths with spaces. If no spaces are found, the original string is returned.
-     * 
+     *
      * @param path string to wrap if containing spaces
      * @return quote wrapped string
      * @deprecated Quoting of command line arguments should be left to the Commandline from plexus-utils.