Index: resteasy-jaxrs/src/test/java/org/jboss/resteasy/spi/ResteasyProviderFactoryTest.java
===================================================================
--- resteasy-jaxrs/src/test/java/org/jboss/resteasy/spi/ResteasyProviderFactoryTest.java	(revision 0)
+++ resteasy-jaxrs/src/test/java/org/jboss/resteasy/spi/ResteasyProviderFactoryTest.java	(revision 0)
@@ -0,0 +1,40 @@
+package org.jboss.resteasy.spi;
+
+import static org.junit.Assert.*;
+
+import java.lang.annotation.Annotation;
+import java.sql.Date;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class ResteasyProviderFactoryTest {
+	
+	private ResteasyProviderFactory factory;
+
+	@Before
+	public void createBean() {
+		factory = new ResteasyProviderFactory();
+	}
+
+	@Test
+	public void shouldReturnStringParameterUnmarshallerAddedForType() {
+		factory.addStringParameterUnmarshaller(MyStringParameterUnmarshaller.class);
+		
+		assertNotNull(factory.createStringParameterUnmarshaller(Date.class));
+	}
+
+	public static class MyStringParameterUnmarshaller implements StringParameterUnmarshaller<Date>{
+
+		@Override
+		public void setAnnotations(Annotation[] annotations) {
+		}
+
+		@Override
+		public Date fromString(String str) {
+			return null;
+		}
+
+	}
+
+}
Index: resteasy-jaxrs/src/main/java/org/jboss/resteasy/spi/ResteasyProviderFactory.java
===================================================================
--- resteasy-jaxrs/src/main/java/org/jboss/resteasy/spi/ResteasyProviderFactory.java	(revision 1415)
+++ resteasy-jaxrs/src/main/java/org/jboss/resteasy/spi/ResteasyProviderFactory.java	(working copy)
@@ -692,7 +692,7 @@
 
    public void addStringParameterUnmarshaller(Class<? extends StringParameterUnmarshaller> provider)
    {
-      Type[] intfs = provider.getClass().getGenericInterfaces();
+      Type[] intfs = provider.getGenericInterfaces();
       for (Type type : intfs)
       {
          if (type instanceof ParameterizedType)