diff --git a/src/main/java/de/neemann/digital/draw/library/ElementLibrary.java b/src/main/java/de/neemann/digital/draw/library/ElementLibrary.java
index 2c1fa6678..5c3d7decb 100644
--- a/src/main/java/de/neemann/digital/draw/library/ElementLibrary.java
+++ b/src/main/java/de/neemann/digital/draw/library/ElementLibrary.java
@@ -153,11 +153,7 @@ public class ElementLibrary implements Iterable<ElementLibrary.ElementContainer>
         node.add(TestCaseElement.TESTCASEDESCRIPTION);
         root.add(node);
 
-        try {
-            populateNodeMap();
-        } catch (IOException e) {
-            // can not happen because there are no custom elements yet
-        }
+        populateNodeMap();
     }
 
     /**
@@ -176,11 +172,9 @@ public class ElementLibrary implements Iterable<ElementLibrary.ElementContainer>
         return customNode;
     }
 
-    private void populateNodeMap() throws IOException {
+    private void populateNodeMap() {
         map.clear();
-        String dn = root.traverse(new PopulateModelVisitor(map)).getDoubleNode();
-        if (dn != null)
-            throw new IOException(Lang.get("err_file_N0_ExistsTwiceBelow_N1", dn, rootLibraryPath));
+        root.traverse(new PopulateMapVisitor(map));
     }
 
     /**
@@ -555,11 +549,10 @@ public class ElementLibrary implements Iterable<ElementLibrary.ElementContainer>
         }
     }
 
-    private static final class PopulateModelVisitor implements Visitor {
+    private static final class PopulateMapVisitor implements Visitor {
         private final HashMap<String, LibraryNode> map;
-        private String doubleNode;
 
-        private PopulateModelVisitor(HashMap<String, LibraryNode> map) {
+        private PopulateMapVisitor(HashMap<String, LibraryNode> map) {
             this.map = map;
         }
 
@@ -568,15 +561,15 @@ public class ElementLibrary implements Iterable<ElementLibrary.ElementContainer>
             if (libraryNode.isLeaf()) {
                 final String name = libraryNode.getName();
 
-                if (map.containsKey(name))
-                    doubleNode = name;
-
-                map.put(name, libraryNode);
+                LibraryNode presentNode = map.get(name);
+                if (presentNode==null) {
+                    map.put(name, libraryNode);
+                    libraryNode.setUnique(true);
+                } else {
+                    presentNode.setUnique(false);
+                    libraryNode.setUnique(false);
+                }
             }
         }
-
-        private String getDoubleNode() {
-            return doubleNode;
-        }
     }
 }
diff --git a/src/main/java/de/neemann/digital/draw/library/LibraryNode.java b/src/main/java/de/neemann/digital/draw/library/LibraryNode.java
index 9bd7d734d..3310a52e7 100644
--- a/src/main/java/de/neemann/digital/draw/library/LibraryNode.java
+++ b/src/main/java/de/neemann/digital/draw/library/LibraryNode.java
@@ -5,6 +5,7 @@ import de.neemann.digital.core.element.ElementTypeDescription;
 import de.neemann.digital.draw.elements.VisualElement;
 import de.neemann.digital.draw.shapes.ShapeFactory;
 import de.neemann.digital.lang.Lang;
+import de.neemann.gui.IconCreator;
 import de.neemann.gui.StringUtils;
 
 import javax.swing.*;
@@ -18,6 +19,7 @@ import java.util.Iterator;
  * Created by hneemann on 25.03.17.
  */
 public class LibraryNode implements Iterable<LibraryNode> {
+    private static final Icon ICON_NOT_UNIQUE = IconCreator.create("testFailed.png");
 
     private final ArrayList<LibraryNode> children;
     private final String translatedName;
@@ -27,6 +29,7 @@ public class LibraryNode implements Iterable<LibraryNode> {
     private ImageIcon icon;
     private ElementLibrary library;
     private LibraryNode parent;
+    private boolean unique;
 
     /**
      * Creates a new node with the given name.
@@ -121,6 +124,9 @@ public class LibraryNode implements Iterable<LibraryNode> {
      */
     public ElementTypeDescription getDescription() throws IOException {
         if (description == null) {
+            if (!unique)
+                throw new IOException(Lang.get("err_file_N0_ExistsTwiceBelow_N1", file, library.getRootFilePath()));
+
             description = library.importElement(file);
             library.fireLibraryChanged(this);
         }
@@ -210,7 +216,7 @@ public class LibraryNode implements Iterable<LibraryNode> {
      * @return the icon
      * @throws IOException IOException
      */
-    public ImageIcon getIcon(ShapeFactory shapeFactory) throws IOException {
+    public Icon getIcon(ShapeFactory shapeFactory) throws IOException {
         getDescription();
         return getIconOrNull(shapeFactory);
     }
@@ -222,10 +228,13 @@ public class LibraryNode implements Iterable<LibraryNode> {
      * @param shapeFactory the shape factory to create the icon
      * @return the icon or null
      */
-    public ImageIcon getIconOrNull(ShapeFactory shapeFactory) {
-        if (icon == null && description != null)
-            icon = new VisualElement(description.getName()).setShapeFactory(shapeFactory).createIcon(75);
-        return icon;
+    public Icon getIconOrNull(ShapeFactory shapeFactory) {
+        if (unique) {
+            if (icon == null && description != null)
+                icon = new VisualElement(description.getName()).setShapeFactory(shapeFactory).createIcon(75);
+            return icon;
+        } else
+            return ICON_NOT_UNIQUE;
     }
 
     /**
@@ -280,11 +289,30 @@ public class LibraryNode implements Iterable<LibraryNode> {
      */
     public String getToolTipText() {
         if (isCustom()) {
-            if (description == null)
-                return null;
-            else
-                return StringUtils.textToHTML(description.getDescription(new ElementAttributes()));
+            if (isUnique()) {
+                if (description == null)
+                    return null;
+                else
+                    return StringUtils.textToHTML(description.getDescription(new ElementAttributes()));
+            } else
+                return Lang.get("msg_fileIsNotUnique");
         } else
             return StringUtils.textToHTML(Lang.getNull("elem_" + getName() + "_tt"));
     }
+
+    /**
+     * sets the unique state of this node
+     *
+     * @param unique true if this node is unique
+     */
+    void setUnique(boolean unique) {
+        this.unique = unique;
+    }
+
+    /**
+     * @return true if element is unique
+     */
+    public boolean isUnique() {
+        return unique;
+    }
 }
diff --git a/src/main/java/de/neemann/digital/gui/InsertAction.java b/src/main/java/de/neemann/digital/gui/InsertAction.java
index 640bbfa9d..8fc929cb3 100644
--- a/src/main/java/de/neemann/digital/gui/InsertAction.java
+++ b/src/main/java/de/neemann/digital/gui/InsertAction.java
@@ -37,6 +37,7 @@ public final class InsertAction extends ToolTipAction {
         this.node = node;
         this.insertHistory = insertHistory;
         this.circuitComponent = circuitComponent;
+        setActive(node.isUnique());
     }
 
     @Override
@@ -76,7 +77,7 @@ public final class InsertAction extends ToolTipAction {
     public void update(LibraryNode node) {
         this.node = node;
         try {
-            final ImageIcon icon = node.getIcon(shapeFactory);
+            final Icon icon = node.getIcon(shapeFactory);
             setIcon(icon);
         } catch (IOException ex) {
             SwingUtilities.invokeLater(new ErrorMessage(Lang.get("msg_errorImportingModel")).addCause(ex));
diff --git a/src/main/java/de/neemann/digital/gui/components/tree/SelectTree.java b/src/main/java/de/neemann/digital/gui/components/tree/SelectTree.java
index 016216ebb..971932f66 100644
--- a/src/main/java/de/neemann/digital/gui/components/tree/SelectTree.java
+++ b/src/main/java/de/neemann/digital/gui/components/tree/SelectTree.java
@@ -43,7 +43,7 @@ public class SelectTree extends JTree {
                 TreePath path = getSelectionPath();
                 if (path != null && path.getPathCount() > 0) {
                     LibraryNode node = (LibraryNode) path.getLastPathComponent();
-                    if (node.isLeaf()) {
+                    if (node.isLeaf() && node.isUnique()) {
                         clearSelection();
                         try {
                             ElementTypeDescription d = node.getDescription();
diff --git a/src/main/resources/lang/lang_de.xml b/src/main/resources/lang/lang_de.xml
index 73ce86986..6f50f94cf 100644
--- a/src/main/resources/lang/lang_de.xml
+++ b/src/main/resources/lang/lang_de.xml
@@ -737,6 +737,7 @@ Die Icons stammen aus dem Tango Desktop Project.</string>
     <string name="msg_startExternalFitter">Starten des externen Fitters</string>
     <string name="msg_actualCircuit">Aktuelle Schaltung</string>
     <string name="msg_fileNotAccessible">Dieser Dateiename ist nicht aus dem aktuellen Projekt importierbar!</string>
+    <string name="msg_fileIsNotUnique">Der Dateiname ist nicht eindeutig!</string>
 
     <string name="ok">Ok</string>
     <string name="rot_0">0°</string>
diff --git a/src/main/resources/lang/lang_en.xml b/src/main/resources/lang/lang_en.xml
index 21754a0a0..888e54a89 100644
--- a/src/main/resources/lang/lang_en.xml
+++ b/src/main/resources/lang/lang_en.xml
@@ -724,6 +724,7 @@ The icons are taken from the Tango Desktop Project.</string>
     <string name="msg_startExternalFitter">Execution of external fitter</string>
     <string name="msg_actualCircuit">Actual Circuit</string>
     <string name="msg_fileNotAccessible">The selected file name is not importable from the actual project!</string>
+    <string name="msg_fileIsNotUnique">The file name is not unique!</string>
 
     <string name="ok">Ok</string>
     <string name="rot_0">0°</string>
diff --git a/src/test/java/de/neemann/digital/core/pld/DiodeTest.java b/src/test/java/de/neemann/digital/core/pld/DiodeTest.java
index a74c528f4..1b04ae125 100644
--- a/src/test/java/de/neemann/digital/core/pld/DiodeTest.java
+++ b/src/test/java/de/neemann/digital/core/pld/DiodeTest.java
@@ -14,11 +14,12 @@ import java.io.IOException;
 public class DiodeTest extends TestCase {
 
     /**
-     * Two antiparallel unidirectional diodes are able to hold each other either in low or in
+     * Two anti parallel unidirectional diodes are able to hold each other either in low or in
      * high state, depending on which diode is processed first.
-     * The current simulation model which is build up on inputs which are modifing the outputs
+     * The current simulation model which is build up on inputs which are modifying the outputs
      * is not suited to handle bidirectional passive diodes.
-     * For the same reason also bidirectional switches are impossible to implement.
+     * The solution implemented for switches - form a common net if switch is closed - is also
+     * not able to handle diodes.
      *
      * To make this possible the simulation core needs a significant improvement.
      */