diff --git a/src/main/java/ru/bclib/api/dataexchange/DataExchangeAPI.java b/src/main/java/ru/bclib/api/dataexchange/DataExchangeAPI.java
index e6029146..0bc6d442 100644
--- a/src/main/java/ru/bclib/api/dataexchange/DataExchangeAPI.java
+++ b/src/main/java/ru/bclib/api/dataexchange/DataExchangeAPI.java
@@ -47,7 +47,8 @@ public class DataExchangeAPI extends DataExchange {
      * @param modID - {@link String} modID.
      */
     public static void registerMod(String modID) {
-        MODS.add(modID);
+        if (!MODS.contains(modID))
+            MODS.add(modID);
     }
 
     /**