diff --git a/src/main/java/org/codehaus/plexus/interpolation/FeedbackingValueSource.java b/src/main/java/org/codehaus/plexus/interpolation/FeedbackingValueSource.java
new file mode 100644
index 0000000..5cb6bdc
--- /dev/null
+++ b/src/main/java/org/codehaus/plexus/interpolation/FeedbackingValueSource.java
@@ -0,0 +1,48 @@
+package org.codehaus.plexus.interpolation;
+
+/*
+ * Copyright 2001-2008 Codehaus Foundation.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Adds feedback on any {@link #getValue(String) getValue(String)} call.
+ * <p>One of the obvious usages is to add FeedbackingValueSource as last value source to {@link Interpolator}
+ * to add feedback messages indicating not resolved expressions.</p>
+ */
+public class FeedbackingValueSource extends AbstractValueSource
+{
+    private final String messagePattern;
+
+    public FeedbackingValueSource()
+    {
+        this( "'${expression}' not resolved" );
+    }
+
+    /**
+     * @param messagePattern could contain <code>${expression}</code> placeholder
+     */
+    public FeedbackingValueSource( String messagePattern )
+    {
+        super( true );
+        this.messagePattern = messagePattern;
+    }
+
+    @Override
+    public Object getValue( String expression )
+    {
+        addFeedback( messagePattern.replace( "${expression}", expression ) );
+        return null;
+    }
+}
diff --git a/src/test/java/org/codehaus/plexus/interpolation/FeedbackingValueSourceTest.java b/src/test/java/org/codehaus/plexus/interpolation/FeedbackingValueSourceTest.java
new file mode 100644
index 0000000..5755e7d
--- /dev/null
+++ b/src/test/java/org/codehaus/plexus/interpolation/FeedbackingValueSourceTest.java
@@ -0,0 +1,62 @@
+package org.codehaus.plexus.interpolation;
+
+/*
+ * Copyright 2001-2008 Codehaus Foundation.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import junit.framework.TestCase;
+
+import static java.util.Collections.singletonMap;
+
+public class FeedbackingValueSourceTest
+    extends TestCase
+{
+
+    public void testStandalone()
+    {
+        ValueSource valueSource = new FeedbackingValueSource();
+        assertNull( valueSource.getValue( "test" ) );
+        assertEquals( 1, valueSource.getFeedback().size() );
+        assertEquals( "'test' not resolved", valueSource.getFeedback().iterator().next() );
+    }
+
+    public void testAfterResolvedExpression() throws InterpolationException
+    {
+        StringSearchInterpolator interpolator = new StringSearchInterpolator();
+        interpolator.addValueSource( new MapBasedValueSource( singletonMap( "key", "val" ) ) );
+        interpolator.addValueSource( new FeedbackingValueSource() );
+        assertEquals( "val", interpolator.interpolate( "${key}" ) );
+        assertTrue( interpolator.getFeedback().isEmpty() );
+    }
+
+    public void testBeforeResolvedExpression() throws InterpolationException
+    {
+        StringSearchInterpolator interpolator = new StringSearchInterpolator();
+        interpolator.addValueSource( new FeedbackingValueSource("Resolving ${expression}") );
+        interpolator.addValueSource( new MapBasedValueSource( singletonMap( "key", "val" ) ) );
+        assertEquals( "val", interpolator.interpolate( "${key}" ) );
+        assertEquals( 1, interpolator.getFeedback().size() );
+        assertEquals( "Resolving key", interpolator.getFeedback().iterator().next() );
+    }
+
+    public void testAfterNotResolvedExpression() throws InterpolationException
+    {
+        StringSearchInterpolator interpolator = new StringSearchInterpolator();
+        interpolator.addValueSource( new MapBasedValueSource( singletonMap( "key", "val" ) ) );
+        interpolator.addValueSource( new FeedbackingValueSource() );
+        assertEquals( "${other-key}", interpolator.interpolate( "${other-key}" ) );
+        assertEquals( 1, interpolator.getFeedback().size() );
+    }
+}