diff --git a/MCGalaxy/util/NET_20.cs b/MCGalaxy/util/NET_20.cs
index 62f9514b9..a7c388a2f 100644
--- a/MCGalaxy/util/NET_20.cs
+++ b/MCGalaxy/util/NET_20.cs
@@ -55,7 +55,7 @@ namespace MCGalaxy.Util {
         }
         
         
-        struct SlimLock : IDisposable {
+        class SlimLock : IDisposable {
             ReaderWriterLock locker;
             bool writeMode;
             
diff --git a/MCGalaxy/util/Threading/IReaderWriterLock.cs b/MCGalaxy/util/Threading/IReaderWriterLock.cs
index 4bbd4fba7..b7f1b47e9 100644
--- a/MCGalaxy/util/Threading/IReaderWriterLock.cs
+++ b/MCGalaxy/util/Threading/IReaderWriterLock.cs
@@ -40,7 +40,7 @@ namespace MCGalaxy.Util {
         }
         
         
-        struct SlimLock : IDisposable {
+        class SlimLock : IDisposable {
             ReaderWriterLockSlim locker;
             bool writeMode;