diff --git a/SMBLibrary/Server/ConnectionState/SMB1Session.cs b/SMBLibrary/Server/ConnectionState/SMB1Session.cs
index fe67675..a7587e5 100644
--- a/SMBLibrary/Server/ConnectionState/SMB1Session.cs
+++ b/SMBLibrary/Server/ConnectionState/SMB1Session.cs
@@ -42,12 +42,15 @@ namespace SMBLibrary.Server
 
         public ushort? AddConnectedTree(ISMBShare share)
         {
-            ushort? treeID = m_connection.AllocateTreeID();
-            if (treeID.HasValue)
+            lock (m_connection)
             {
-                m_connectedTrees.Add(treeID.Value, share);
+                ushort? treeID = m_connection.AllocateTreeID();
+                if (treeID.HasValue)
+                {
+                    m_connectedTrees.Add(treeID.Value, share);
+                }
+                return treeID;
             }
-            return treeID;
         }
 
         public ISMBShare GetConnectedTree(ushort treeID)
@@ -63,7 +66,7 @@ namespace SMBLibrary.Server
             m_connectedTrees.TryGetValue(treeID, out share);
             if (share != null)
             {
-                lock (m_openFiles)
+                lock (m_connection)
                 {
                     List<ushort> fileIDList = new List<ushort>(m_openFiles.Keys);
                     foreach (ushort fileID in fileIDList)
@@ -75,8 +78,8 @@ namespace SMBLibrary.Server
                             m_openFiles.Remove(fileID);
                         }
                     }
+                    m_connectedTrees.Remove(treeID);
                 }
-                m_connectedTrees.Remove(treeID);
             }
         }
 
@@ -94,15 +97,15 @@ namespace SMBLibrary.Server
 
         public ushort? AddOpenFile(ushort treeID, string shareName, string relativePath, object handle)
         {
-            ushort? fileID = m_connection.AllocateFileID();
-            if (fileID.HasValue)
+            lock (m_connection)
             {
-                lock (m_openFiles)
+                ushort? fileID = m_connection.AllocateFileID();
+                if (fileID.HasValue)
                 {
                     m_openFiles.Add(fileID.Value, new OpenFileObject(treeID, shareName, relativePath, handle));
                 }
+                return fileID;
             }
-            return fileID;
         }
 
         public OpenFileObject GetOpenFileObject(ushort fileID)
@@ -114,7 +117,7 @@ namespace SMBLibrary.Server
 
         public void RemoveOpenFile(ushort fileID)
         {
-            lock (m_openFiles)
+            lock (m_connection)
             {
                 m_openFiles.Remove(fileID);
             }
@@ -123,7 +126,7 @@ namespace SMBLibrary.Server
         public List<string> ListOpenFiles()
         {
             List<string> result = new List<string>();
-            lock (m_openFiles)
+            lock (m_connection)
             {
                 foreach (OpenFileObject openFile in m_openFiles.Values)
                 {
diff --git a/SMBLibrary/Server/ConnectionState/SMB2Session.cs b/SMBLibrary/Server/ConnectionState/SMB2Session.cs
index cea9bc8..f90c8b8 100644
--- a/SMBLibrary/Server/ConnectionState/SMB2Session.cs
+++ b/SMBLibrary/Server/ConnectionState/SMB2Session.cs
@@ -62,24 +62,22 @@ namespace SMBLibrary.Server
 
         public uint? AddConnectedTree(ISMBShare share)
         {
-            uint? treeID = AllocateTreeID();
-            if (treeID.HasValue)
+            lock (m_connectedTrees)
             {
-                m_connectedTrees.Add(treeID.Value, share);
+                uint? treeID = AllocateTreeID();
+                if (treeID.HasValue)
+                {
+                    m_connectedTrees.Add(treeID.Value, share);
+                }
+                return treeID;
             }
-            return treeID;
         }
 
         public ISMBShare GetConnectedTree(uint treeID)
         {
-            if (m_connectedTrees.ContainsKey(treeID))
-            {
-                return m_connectedTrees[treeID];
-            }
-            else
-            {
-                return null;
-            }
+            ISMBShare result;
+            m_connectedTrees.TryGetValue(treeID, out result);
+            return result;
         }
 
         public void DisconnectTree(uint treeID)
@@ -101,7 +99,10 @@ namespace SMBLibrary.Server
                         }
                     }
                 }
-                m_connectedTrees.Remove(treeID);
+                lock (m_connectedTrees)
+                {
+                    m_connectedTrees.Remove(treeID);
+                }
             }
         }
 
@@ -131,19 +132,19 @@ namespace SMBLibrary.Server
 
         public FileID? AddOpenFile(uint treeID, string shareName, string relativePath, object handle)
         {
-            ulong? volatileFileID = AllocateVolatileFileID();
-            if (volatileFileID.HasValue)
+            lock (m_openFiles)
             {
-                FileID fileID = new FileID();
-                fileID.Volatile = volatileFileID.Value;
-                // [MS-SMB2] FileId.Persistent MUST be set to Open.DurableFileId.
-                // Note: We don't support durable handles so we use volatileFileID.
-                fileID.Persistent = volatileFileID.Value;
-                lock (m_openFiles)
+                ulong? volatileFileID = AllocateVolatileFileID();
+                if (volatileFileID.HasValue)
                 {
+                    FileID fileID = new FileID();
+                    fileID.Volatile = volatileFileID.Value;
+                    // [MS-SMB2] FileId.Persistent MUST be set to Open.DurableFileId.
+                    // Note: We don't support durable handles so we use volatileFileID.
+                    fileID.Persistent = volatileFileID.Value;
                     m_openFiles.Add(volatileFileID.Value, new OpenFileObject(treeID, shareName, relativePath, handle));
+                    return fileID;
                 }
-                return fileID;
             }
             return null;
         }