diff --git a/runelite-client/src/main/java/net/runelite/client/game/ItemManager.java b/runelite-client/src/main/java/net/runelite/client/game/ItemManager.java
index 3832cea464..764b30ddfe 100644
--- a/runelite-client/src/main/java/net/runelite/client/game/ItemManager.java
+++ b/runelite-client/src/main/java/net/runelite/client/game/ItemManager.java
@@ -204,6 +204,7 @@ public class ItemManager
 	 */
 	public ItemComposition getItemComposition(int itemId)
 	{
+		assert client.isClientThread() : "getItemComposition must be called on client thread";
 		return itemCompositions.getUnchecked(itemId);
 	}