diff --git a/src/main/java/com/inteligr8/maven/aps/modeling/util/Index.java b/src/main/java/com/inteligr8/maven/aps/modeling/util/Index.java
index 2089be8..77fd021 100644
--- a/src/main/java/com/inteligr8/maven/aps/modeling/util/Index.java
+++ b/src/main/java/com/inteligr8/maven/aps/modeling/util/Index.java
@@ -132,6 +132,11 @@ public class Index<K, V> {
 	 * @return true if the key already existed and was overwritten; false otherwise.
 	 */
 	public synchronized boolean put(K key, V value) {
+		if (key == null)
+			throw new IllegalArgumentException("An index key may not be null");
+		if (value == null)
+			throw new IllegalArgumentException("An index value may not be null");
+		
 		boolean overwrote = false;
 		
 		V oldValue = this.forwardMap.get(key);
@@ -159,6 +164,9 @@ public class Index<K, V> {
 	 * @return true if the key and its value were removed; false otherwise.
 	 */
 	public synchronized boolean remove(K key) {
+		if (key == null)
+			throw new IllegalArgumentException("An index key may not be null");
+		
 		V oldValue = this.forwardMap.remove(key);
 		if (oldValue == null)
 			return false;