diff --git a/maven-artifact/src/main/java/org/apache/maven/artifact/factory/ArtifactFactory.java b/maven-artifact/src/main/java/org/apache/maven/artifact/factory/ArtifactFactory.java
index fbc7423e23..e85bfaec0c 100644
--- a/maven-artifact/src/main/java/org/apache/maven/artifact/factory/ArtifactFactory.java
+++ b/maven-artifact/src/main/java/org/apache/maven/artifact/factory/ArtifactFactory.java
@@ -57,5 +57,5 @@ public interface ArtifactFactory
 
     Artifact createProjectArtifact( String groupId, String artifactId, String version, String scope );
 
-    Artifact createExtensionArtifact( String groupId, String artifactId, String version );
+    Artifact createExtensionArtifact( String groupId, String artifactId, VersionRange versionRange );
 }
diff --git a/maven-artifact/src/main/java/org/apache/maven/artifact/factory/DefaultArtifactFactory.java b/maven-artifact/src/main/java/org/apache/maven/artifact/factory/DefaultArtifactFactory.java
index 39a9f277f5..ac131ea73f 100644
--- a/maven-artifact/src/main/java/org/apache/maven/artifact/factory/DefaultArtifactFactory.java
+++ b/maven-artifact/src/main/java/org/apache/maven/artifact/factory/DefaultArtifactFactory.java
@@ -86,9 +86,9 @@ public class DefaultArtifactFactory
         return createArtifact( groupId, artifactId, version, scope, "pom" );
     }
 
-    public Artifact createExtensionArtifact( String groupId, String artifactId, String version )
+    public Artifact createExtensionArtifact( String groupId, String artifactId, VersionRange versionRange )
     {
-        return createArtifact( groupId, artifactId, version, Artifact.SCOPE_RUNTIME, "jar" );
+        return createArtifact( groupId, artifactId, versionRange, Artifact.SCOPE_RUNTIME, "jar", null, null );
     }
 
     public Artifact createArtifact( String groupId, String artifactId, String version, String scope, String type,
diff --git a/maven-core/src/main/java/org/apache/maven/extension/DefaultExtensionManager.java b/maven-core/src/main/java/org/apache/maven/extension/DefaultExtensionManager.java
index 8099f1cc66..06ee36bc68 100644
--- a/maven-core/src/main/java/org/apache/maven/extension/DefaultExtensionManager.java
+++ b/maven-core/src/main/java/org/apache/maven/extension/DefaultExtensionManager.java
@@ -23,6 +23,8 @@ import org.apache.maven.artifact.repository.ArtifactRepository;
 import org.apache.maven.artifact.resolver.ArtifactResolutionException;
 import org.apache.maven.artifact.resolver.ArtifactResolutionResult;
 import org.apache.maven.artifact.resolver.ArtifactResolver;
+import org.apache.maven.artifact.versioning.InvalidVersionSpecificationException;
+import org.apache.maven.artifact.versioning.VersionRange;
 import org.apache.maven.model.Extension;
 import org.apache.maven.project.MavenProject;
 import org.codehaus.plexus.PlexusConstants;
@@ -31,6 +33,7 @@ import org.codehaus.plexus.PlexusContainerException;
 import org.codehaus.plexus.context.Context;
 import org.codehaus.plexus.context.ContextException;
 import org.codehaus.plexus.personality.plexus.lifecycle.phase.Contextualizable;
+import org.codehaus.plexus.util.StringUtils;
 
 import java.util.Collections;
 import java.util.Iterator;
@@ -53,21 +56,36 @@ public class DefaultExtensionManager
     private PlexusContainer container;
 
     public void addExtension( Extension extension, MavenProject project, ArtifactRepository localRepository )
-        throws ArtifactResolutionException, PlexusContainerException
+        throws ArtifactResolutionException, PlexusContainerException, InvalidVersionSpecificationException
     {
-        // TODO: version may be null
-        Artifact artifact = artifactFactory.createExtensionArtifact( extension.getGroupId(), extension.getArtifactId(),
-                                                                     extension.getVersion() );
+        // TODO: this is duplicated with DefaultMavenProjectBuilder. Push into artifact factory.
+        String version;
 
-        ArtifactResolutionResult result = artifactResolver.resolveTransitively( Collections.singleton( artifact ),
-                                                                                project.getArtifact(),
-                                                                                project.getRemoteArtifactRepositories(),
-                                                                                localRepository,
-                                                                                artifactMetadataSource );
-        for ( Iterator i = result.getArtifacts().iterator(); i.hasNext(); )
+        if ( StringUtils.isEmpty( extension.getVersion() ) )
         {
-            Artifact a = (Artifact) i.next();
-            container.addJarResource( a.getFile() );
+            version = "RELEASE";
+        }
+        else
+        {
+            version = extension.getVersion();
+        }
+
+        VersionRange versionRange = VersionRange.createFromVersionSpec( version );
+        Artifact artifact = artifactFactory.createExtensionArtifact( extension.getGroupId(), extension.getArtifactId(),
+                                                                     versionRange );
+
+        if ( artifact != null )
+        {
+            ArtifactResolutionResult result = artifactResolver.resolveTransitively( Collections.singleton( artifact ),
+                                                                                    project.getArtifact(),
+                                                                                    project.getRemoteArtifactRepositories(),
+                                                                                    localRepository,
+                                                                                    artifactMetadataSource );
+            for ( Iterator i = result.getArtifacts().iterator(); i.hasNext(); )
+            {
+                Artifact a = (Artifact) i.next();
+                container.addJarResource( a.getFile() );
+            }
         }
     }
 
diff --git a/maven-core/src/main/java/org/apache/maven/extension/ExtensionManager.java b/maven-core/src/main/java/org/apache/maven/extension/ExtensionManager.java
index fce6a030b4..88bffc2584 100644
--- a/maven-core/src/main/java/org/apache/maven/extension/ExtensionManager.java
+++ b/maven-core/src/main/java/org/apache/maven/extension/ExtensionManager.java
@@ -18,6 +18,7 @@ package org.apache.maven.extension;
 
 import org.apache.maven.artifact.repository.ArtifactRepository;
 import org.apache.maven.artifact.resolver.ArtifactResolutionException;
+import org.apache.maven.artifact.versioning.InvalidVersionSpecificationException;
 import org.apache.maven.model.Extension;
 import org.apache.maven.project.MavenProject;
 import org.codehaus.plexus.PlexusContainerException;
@@ -31,5 +32,5 @@ import org.codehaus.plexus.PlexusContainerException;
 public interface ExtensionManager
 {
     void addExtension( Extension extension, MavenProject project, ArtifactRepository localRepository )
-        throws ArtifactResolutionException, PlexusContainerException;
+        throws ArtifactResolutionException, PlexusContainerException, InvalidVersionSpecificationException;
 }
diff --git a/maven-core/src/main/java/org/apache/maven/lifecycle/DefaultLifecycleExecutor.java b/maven-core/src/main/java/org/apache/maven/lifecycle/DefaultLifecycleExecutor.java
index ffc0417402..6eb5838594 100644
--- a/maven-core/src/main/java/org/apache/maven/lifecycle/DefaultLifecycleExecutor.java
+++ b/maven-core/src/main/java/org/apache/maven/lifecycle/DefaultLifecycleExecutor.java
@@ -16,10 +16,11 @@ package org.apache.maven.lifecycle;
  * limitations under the License.
  */
 
-import org.apache.maven.artifact.repository.ArtifactRepository;
-import org.apache.maven.artifact.resolver.ArtifactResolutionException;
 import org.apache.maven.artifact.handler.ArtifactHandler;
 import org.apache.maven.artifact.handler.manager.ArtifactHandlerManager;
+import org.apache.maven.artifact.repository.ArtifactRepository;
+import org.apache.maven.artifact.resolver.ArtifactResolutionException;
+import org.apache.maven.artifact.versioning.InvalidVersionSpecificationException;
 import org.apache.maven.execution.MavenExecutionResponse;
 import org.apache.maven.execution.MavenSession;
 import org.apache.maven.extension.ExtensionManager;
@@ -144,6 +145,10 @@ public class DefaultLifecycleExecutor
         {
             throw new LifecycleExecutionException( "Unable to initialise extensions", e );
         }
+        catch ( InvalidVersionSpecificationException e )
+        {
+            throw new LifecycleExecutionException( "Unable to initialise extensions", e );
+        }
         finally
         {
             response.setFinish( new Date() );