diff --git a/parent/pom.xml b/parent/pom.xml
index 3df2cd45c..2076e2169 100644
--- a/parent/pom.xml
+++ b/parent/pom.xml
@@ -82,6 +82,11 @@
                 <artifactId>fest-assert</artifactId>
                 <version>1.4</version>
             </dependency>
+            <dependency>
+                <groupId>com.google.guava</groupId>
+                <artifactId>guava</artifactId>
+                <version>14.0.1</version>
+            </dependency>
             <dependency>
                 <groupId>com.jolira</groupId>
                 <artifactId>hickory</artifactId>
diff --git a/processor/pom.xml b/processor/pom.xml
index 28cda2df0..8cf7d2bfd 100644
--- a/processor/pom.xml
+++ b/processor/pom.xml
@@ -61,6 +61,11 @@
             <artifactId>fest-assert</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>
diff --git a/processor/src/main/java/org/mapstruct/ap/MapperGenerationVisitor.java b/processor/src/main/java/org/mapstruct/ap/MapperGenerationVisitor.java
index 7d84395c5..59106ebf4 100644
--- a/processor/src/main/java/org/mapstruct/ap/MapperGenerationVisitor.java
+++ b/processor/src/main/java/org/mapstruct/ap/MapperGenerationVisitor.java
@@ -34,6 +34,7 @@ import javax.lang.model.type.TypeMirror;
 import javax.lang.model.util.ElementKindVisitor6;
 import javax.lang.model.util.Elements;
 import javax.lang.model.util.Types;
+import javax.tools.Diagnostic.Kind;
 import javax.tools.JavaFileObject;
 
 import org.mapstruct.ap.conversion.Conversion;
@@ -308,6 +309,26 @@ public class MapperGenerationVisitor extends ElementKindVisitor6<Void, Void> {
                     properties
                 )
             );
+
+            if ( declaringMapper == null ) {
+                if ( parameter.getType().isIterableType() && !returnType.isIterableType() ) {
+                    processingEnvironment.getMessager()
+                        .printMessage(
+                            Kind.ERROR,
+                            "Can't generate mapping method from iterable type to non-iterable ype.",
+                            method
+                        );
+                }
+
+                if ( !parameter.getType().isIterableType() && returnType.isIterableType() ) {
+                    processingEnvironment.getMessager()
+                        .printMessage(
+                            Kind.ERROR,
+                            "Can't generate mapping method from non-iterable type to iterable ype.",
+                            method
+                        );
+                }
+            }
         }
 
         MapperPrism mapperPrism = MapperPrism.getInstanceOn( element );
diff --git a/processor/src/test/java/org/mapstruct/ap/test/collection/erronuous/ErronuousCollectionMappingTest.java b/processor/src/test/java/org/mapstruct/ap/test/collection/erronuous/ErronuousCollectionMappingTest.java
new file mode 100644
index 000000000..6e78daa71
--- /dev/null
+++ b/processor/src/test/java/org/mapstruct/ap/test/collection/erronuous/ErronuousCollectionMappingTest.java
@@ -0,0 +1,42 @@
+/**
+ *  Copyright 2012-2013 Gunnar Morling (http://www.gunnarmorling.de/)
+ *
+ *  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.
+ */
+package org.mapstruct.ap.test.collection.erronuous;
+
+import javax.tools.Diagnostic.Kind;
+
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.MapperTestBase;
+import org.mapstruct.ap.testutil.WithClasses;
+import org.mapstruct.ap.testutil.compilation.annotation.CompilationResult;
+import org.mapstruct.ap.testutil.compilation.annotation.Diagnostic;
+import org.mapstruct.ap.testutil.compilation.annotation.ExpectedCompilationOutcome;
+import org.testng.annotations.Test;
+
+@WithClasses({ ErronuousMapper.class })
+public class ErronuousCollectionMappingTest extends MapperTestBase {
+
+    @Test
+    @IssueKey("6")
+    @ExpectedCompilationOutcome(
+        value = CompilationResult.FAILED,
+        diagnostics = {
+            @Diagnostic(type = ErronuousMapper.class, kind = Kind.ERROR, line = 25),
+            @Diagnostic(type = ErronuousMapper.class, kind = Kind.ERROR, line = 27)
+        }
+    )
+    public void shouldFailToGenerateMappingFromListToString() {
+    }
+}
diff --git a/processor/src/test/java/org/mapstruct/ap/test/collection/erronuous/ErronuousMapper.java b/processor/src/test/java/org/mapstruct/ap/test/collection/erronuous/ErronuousMapper.java
new file mode 100644
index 000000000..9eaf9a22e
--- /dev/null
+++ b/processor/src/test/java/org/mapstruct/ap/test/collection/erronuous/ErronuousMapper.java
@@ -0,0 +1,28 @@
+/**
+ *  Copyright 2012-2013 Gunnar Morling (http://www.gunnarmorling.de/)
+ *
+ *  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.
+ */
+package org.mapstruct.ap.test.collection.erronuous;
+
+import java.util.Set;
+
+import org.mapstruct.Mapper;
+
+@Mapper
+public interface ErronuousMapper {
+
+    Integer stringSetToInteger(Set<String> strings);
+
+    Set<String> integerToStringSet(Integer integer);
+}
diff --git a/processor/src/test/java/org/mapstruct/ap/test/collection/iterabletononiterable/IterableToNonIterableMappingTest.java b/processor/src/test/java/org/mapstruct/ap/test/collection/iterabletononiterable/IterableToNonIterableMappingTest.java
new file mode 100644
index 000000000..6afe868eb
--- /dev/null
+++ b/processor/src/test/java/org/mapstruct/ap/test/collection/iterabletononiterable/IterableToNonIterableMappingTest.java
@@ -0,0 +1,52 @@
+/**
+ *  Copyright 2012-2013 Gunnar Morling (http://www.gunnarmorling.de/)
+ *
+ *  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.
+ */
+package org.mapstruct.ap.test.collection.iterabletononiterable;
+
+import java.util.Arrays;
+
+import org.mapstruct.ap.testutil.IssueKey;
+import org.mapstruct.ap.testutil.MapperTestBase;
+import org.mapstruct.ap.testutil.WithClasses;
+import org.testng.annotations.Test;
+
+import static org.fest.assertions.Assertions.assertThat;
+
+@WithClasses({ Source.class, Target.class, SourceTargetMapper.class, StringListMapper.class })
+public class IterableToNonIterableMappingTest extends MapperTestBase {
+
+    @Test
+    @IssueKey("6")
+    public void shouldMapStringListToStringUsingCustomMapper() {
+        Source source = new Source();
+        source.setNames( Arrays.asList( "Alice", "Bob", "Jim" ) );
+        Target target = SourceTargetMapper.INSTANCE.sourceToTarget( source );
+
+        assertThat( target ).isNotNull();
+        assertThat( target.getNames() ).isEqualTo( "Alice-Bob-Jim" );
+    }
+
+    @Test
+    @IssueKey("6")
+    public void shouldReverseMapStringListToStringUsingCustomMapper() {
+        Target target = new Target();
+        target.setNames( "Alice-Bob-Jim" );
+
+        Source source = SourceTargetMapper.INSTANCE.targetToSource( target );
+
+        assertThat( source ).isNotNull();
+        assertThat( source.getNames() ).isEqualTo( Arrays.asList( "Alice", "Bob", "Jim" ) );
+    }
+}
diff --git a/processor/src/test/java/org/mapstruct/ap/test/collection/iterabletononiterable/Source.java b/processor/src/test/java/org/mapstruct/ap/test/collection/iterabletononiterable/Source.java
new file mode 100644
index 000000000..91268f967
--- /dev/null
+++ b/processor/src/test/java/org/mapstruct/ap/test/collection/iterabletononiterable/Source.java
@@ -0,0 +1,31 @@
+/**
+ *  Copyright 2012-2013 Gunnar Morling (http://www.gunnarmorling.de/)
+ *
+ *  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.
+ */
+package org.mapstruct.ap.test.collection.iterabletononiterable;
+
+import java.util.List;
+
+public class Source {
+
+    private List<String> names;
+
+    public List<String> getNames() {
+        return names;
+    }
+
+    public void setNames(List<String> names) {
+        this.names = names;
+    }
+}
diff --git a/processor/src/test/java/org/mapstruct/ap/test/collection/iterabletononiterable/SourceTargetMapper.java b/processor/src/test/java/org/mapstruct/ap/test/collection/iterabletononiterable/SourceTargetMapper.java
new file mode 100644
index 000000000..84890e492
--- /dev/null
+++ b/processor/src/test/java/org/mapstruct/ap/test/collection/iterabletononiterable/SourceTargetMapper.java
@@ -0,0 +1,29 @@
+/**
+ *  Copyright 2012-2013 Gunnar Morling (http://www.gunnarmorling.de/)
+ *
+ *  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.
+ */
+package org.mapstruct.ap.test.collection.iterabletononiterable;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.Mappers;
+
+@Mapper(uses = StringListMapper.class)
+public interface SourceTargetMapper {
+
+    public static SourceTargetMapper INSTANCE = Mappers.getMapper( SourceTargetMapper.class );
+
+    Target sourceToTarget(Source source);
+
+    Source targetToSource(Target target);
+}
diff --git a/processor/src/test/java/org/mapstruct/ap/test/collection/iterabletononiterable/StringListMapper.java b/processor/src/test/java/org/mapstruct/ap/test/collection/iterabletononiterable/StringListMapper.java
new file mode 100644
index 000000000..c362efc1d
--- /dev/null
+++ b/processor/src/test/java/org/mapstruct/ap/test/collection/iterabletononiterable/StringListMapper.java
@@ -0,0 +1,32 @@
+/**
+ *  Copyright 2012-2013 Gunnar Morling (http://www.gunnarmorling.de/)
+ *
+ *  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.
+ */
+package org.mapstruct.ap.test.collection.iterabletononiterable;
+
+import java.util.Arrays;
+import java.util.List;
+
+import com.google.common.base.Joiner;
+
+public class StringListMapper {
+
+    public String stringListToString(List<String> strings) {
+        return strings == null ? null : Joiner.on( "-" ).join( strings );
+    }
+
+    public List<String> stringToStringList(String string) {
+        return string == null ? null : Arrays.asList( string.split( "-" ) );
+    }
+}
diff --git a/processor/src/test/java/org/mapstruct/ap/test/collection/iterabletononiterable/Target.java b/processor/src/test/java/org/mapstruct/ap/test/collection/iterabletononiterable/Target.java
new file mode 100644
index 000000000..00cd2ebd3
--- /dev/null
+++ b/processor/src/test/java/org/mapstruct/ap/test/collection/iterabletononiterable/Target.java
@@ -0,0 +1,29 @@
+/**
+ *  Copyright 2012-2013 Gunnar Morling (http://www.gunnarmorling.de/)
+ *
+ *  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.
+ */
+package org.mapstruct.ap.test.collection.iterabletononiterable;
+
+public class Target {
+
+    private String names;
+
+    public String getNames() {
+        return names;
+    }
+
+    public void setNames(String names) {
+        this.names = names;
+    }
+}
diff --git a/processor/src/test/java/org/mapstruct/ap/testutil/MapperTestBase.java b/processor/src/test/java/org/mapstruct/ap/testutil/MapperTestBase.java
index c15e9726a..a72c024da 100644
--- a/processor/src/test/java/org/mapstruct/ap/testutil/MapperTestBase.java
+++ b/processor/src/test/java/org/mapstruct/ap/testutil/MapperTestBase.java
@@ -59,7 +59,7 @@ public abstract class MapperTestBase {
     private DiagnosticCollector<JavaFileObject> diagnostics;
 
     public MapperTestBase() {
-        this.libraries = Arrays.asList( "mapstruct.jar" );
+        this.libraries = Arrays.asList( "mapstruct.jar", "guava.jar" );
     }
 
     @BeforeClass
@@ -107,7 +107,7 @@ public abstract class MapperTestBase {
 
         if ( expectedResult.getCompilationResult() == CompilationResult.SUCCEEDED ) {
             assertThat( actualResult.getCompilationResult() )
-                .describedAs( "Compilation failed. Diagnostics: " + actualResult.getDiagnostics() )
+                .describedAs( "Compilation failed. Diagnostics: " + diagnostics.getDiagnostics() )
                 .isEqualTo( CompilationResult.SUCCEEDED );
         }
         else {
diff --git a/processor/src/test/java/org/mapstruct/ap/testutil/compilation/model/CompilationOutcomeDescriptor.java b/processor/src/test/java/org/mapstruct/ap/testutil/compilation/model/CompilationOutcomeDescriptor.java
index 0938a943d..fc70f097f 100644
--- a/processor/src/test/java/org/mapstruct/ap/testutil/compilation/model/CompilationOutcomeDescriptor.java
+++ b/processor/src/test/java/org/mapstruct/ap/testutil/compilation/model/CompilationOutcomeDescriptor.java
@@ -19,6 +19,7 @@ import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
+import javax.tools.Diagnostic.Kind;
 import javax.tools.JavaFileObject;
 
 import org.mapstruct.ap.testutil.compilation.annotation.CompilationResult;
@@ -63,7 +64,10 @@ public class CompilationOutcomeDescriptor {
 
         Set<DiagnosticDescriptor> diagnosticDescriptors = new HashSet<DiagnosticDescriptor>();
         for ( javax.tools.Diagnostic<? extends JavaFileObject> diagnostic : diagnostics ) {
-            diagnosticDescriptors.add( DiagnosticDescriptor.forDiagnostic( sourceDir, diagnostic ) );
+            //ignore notes created by the compiler
+            if ( diagnostic.getKind() != Kind.NOTE ) {
+                diagnosticDescriptors.add( DiagnosticDescriptor.forDiagnostic( sourceDir, diagnostic ) );
+            }
         }
 
         return new CompilationOutcomeDescriptor( compilationResult, diagnosticDescriptors );