diff --git a/scm-core/src/main/java/sonia/scm/plugin/PluginConditionFailedException.java b/scm-core/src/main/java/sonia/scm/plugin/PluginConditionFailedException.java
new file mode 100644
index 0000000000..bbee261d54
--- /dev/null
+++ b/scm-core/src/main/java/sonia/scm/plugin/PluginConditionFailedException.java
@@ -0,0 +1,89 @@
+/**
+ * Copyright (c) 2010, Sebastian Sdorra 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. Neither the name of SCM-Manager;
+ * nor the names of its contributors may be used to endorse or promote products
+ * derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS 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 REGENTS OR 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.
+ *
+ * http://bitbucket.org/sdorra/scm-manager
+ *
+ */
+
+
+
+package sonia.scm.plugin;
+
+/**
+ *
+ * @author Sebastian Sdorra
+ * @since 1.21
+ */
+public final class PluginConditionFailedException extends PluginException
+{
+
+  /** Field description */
+  private static final long serialVersionUID = 3257937172323964102L;
+
+  //~--- constructors ---------------------------------------------------------
+
+  /**
+   * Constructs ...
+   *
+   *
+   * @param condition
+   */
+  public PluginConditionFailedException(PluginCondition condition)
+  {
+    this.condition = condition;
+  }
+
+  /**
+   *  Constructs ...
+   * 
+   * 
+   *  @param condition
+   * @param message
+   */
+  public PluginConditionFailedException(PluginCondition condition,
+    String message)
+  {
+    super(message);
+    this.condition = condition;
+  }
+
+  //~--- get methods ----------------------------------------------------------
+
+  /**
+   * Method description
+   *
+   *
+   * @return
+   */
+  public PluginCondition getCondition()
+  {
+    return condition;
+  }
+
+  //~--- fields ---------------------------------------------------------------
+
+  /** Field description */
+  private PluginCondition condition;
+}
diff --git a/scm-webapp/src/main/java/sonia/scm/api/rest/resources/PluginResource.java b/scm-webapp/src/main/java/sonia/scm/api/rest/resources/PluginResource.java
index 4996c8fe98..e94fd70e42 100644
--- a/scm-webapp/src/main/java/sonia/scm/api/rest/resources/PluginResource.java
+++ b/scm-webapp/src/main/java/sonia/scm/api/rest/resources/PluginResource.java
@@ -40,8 +40,12 @@ import com.google.inject.Singleton;
 
 import org.codehaus.enunciate.modules.jersey.ExternallyManagedLifecycle;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import sonia.scm.plugin.DefaultPluginManager;
 import sonia.scm.plugin.OverviewPluginFilter;
+import sonia.scm.plugin.PluginConditionFailedException;
 import sonia.scm.plugin.PluginInformation;
 import sonia.scm.plugin.PluginInformationComparator;
 
@@ -66,6 +70,7 @@ import javax.ws.rs.PathParam;
 import javax.ws.rs.Produces;
 import javax.ws.rs.core.MediaType;
 import javax.ws.rs.core.Response;
+import javax.ws.rs.core.Response.Status;
 
 /**
  *
@@ -77,6 +82,14 @@ import javax.ws.rs.core.Response;
 public class PluginResource
 {
 
+  /**
+   * the logger for PluginResource
+   */
+  private static final Logger logger =
+    LoggerFactory.getLogger(PluginResource.class);
+
+  //~--- constructors ---------------------------------------------------------
+
   /**
    * Constructs ...
    *
@@ -96,6 +109,7 @@ public class PluginResource
    * <br />
    * <ul>
    *   <li>200 success</li>
+   *   <li>412 conflict</li>
    *   <li>500 internal server error</li>
    * </ul>
    *
@@ -113,9 +127,21 @@ public class PluginResource
     @FormDataParam("package") InputStream uploadedInputStream)
     throws IOException
   {
-    pluginManager.installPackage(uploadedInputStream);
+    Response response = null;
 
-    return Response.ok().build();
+    try
+    {
+      pluginManager.installPackage(uploadedInputStream);
+      response = Response.ok().build();
+    }
+    catch (PluginConditionFailedException ex)
+    {
+      logger.warn(
+        "could not install plugin package, because the condition failed", ex);
+      response = Response.status(Status.CONFLICT).build();
+    }
+
+    return response;
   }
 
   /**
diff --git a/scm-webapp/src/main/java/sonia/scm/plugin/DefaultPluginManager.java b/scm-webapp/src/main/java/sonia/scm/plugin/DefaultPluginManager.java
index 7d7205cf87..35ee52c115 100644
--- a/scm-webapp/src/main/java/sonia/scm/plugin/DefaultPluginManager.java
+++ b/scm-webapp/src/main/java/sonia/scm/plugin/DefaultPluginManager.java
@@ -240,9 +240,13 @@ public class DefaultPluginManager
 
       Plugin plugin = JAXB.unmarshal(new File(tempDirectory, "plugin.xml"),
                         Plugin.class);
-      
-      // TODO check conditions
-      
+
+      PluginCondition condition = plugin.getCondition();
+
+      if ((condition != null) &&!condition.isSupported())
+      {
+        throw new PluginConditionFailedException(condition);
+      }
 
       AetherPluginHandler aph = new AetherPluginHandler(this, context,
                                   configuration);