diff --git a/src/dorkbox/util/collections/LockFreeIntBiMap.java b/src/dorkbox/util/collections/LockFreeIntBiMap.java
index 07475f0..2d922dd 100644
--- a/src/dorkbox/util/collections/LockFreeIntBiMap.java
+++ b/src/dorkbox/util/collections/LockFreeIntBiMap.java
@@ -300,7 +300,9 @@ class LockFreeIntBiMap<V> {
     public synchronized
     V remove(final int key) {
         V value = forwardHashMap.remove(key);
-        reverseHashMap.remove(value, defaultReturnValue);
+        if (value != null) {
+            reverseHashMap.remove(value, defaultReturnValue);
+        }
         return value;
     }
 
diff --git a/src/dorkbox/util/collections/LockFreeObjectIntBiMap.java b/src/dorkbox/util/collections/LockFreeObjectIntBiMap.java
index cf40ef0..55cd158 100644
--- a/src/dorkbox/util/collections/LockFreeObjectIntBiMap.java
+++ b/src/dorkbox/util/collections/LockFreeObjectIntBiMap.java
@@ -276,7 +276,9 @@ class LockFreeObjectIntBiMap<V> {
     public synchronized
     int remove(final V key) {
         int value = forwardHashMap.remove(key, defaultReturnValue);
-        reverseHashMap.remove(value);
+        if (value != defaultReturnValue) {
+            reverseHashMap.remove(value);
+        }
         return value;
     }