diff --git a/src/com/esotericsoftware/kryo/util/IdentityObjectIntMap.java b/src/com/esotericsoftware/kryo/util/IdentityObjectIntMap.java
index d2dea0ffc..b5002a1e6 100644
--- a/src/com/esotericsoftware/kryo/util/IdentityObjectIntMap.java
+++ b/src/com/esotericsoftware/kryo/util/IdentityObjectIntMap.java
@@ -524,6 +524,8 @@ public void ensureCapacity (int additionalCapacity) {
 	}
 
 	private void resize (int newSize) {
+		if (newSize < 0) throw new IllegalArgumentException("newSize must be >= 0: " + newSize);
+
 		int oldEndIndex = capacity + stashSize;
 
 		capacity = newSize;