diff --git a/session/SessionCache.cs b/session/SessionCache.cs
index e125256..3d875af 100644
--- a/session/SessionCache.cs
+++ b/session/SessionCache.cs
@@ -53,14 +53,20 @@ namespace ln.http.resources.session
             Guid sessionID = FindSessionID(httpRequest);
             if (!Guid.Empty.Equals(sessionID) && Contains(sessionID))
             {
-                Session session = this.sessions[sessionID];
-                session.Touch();
-                return session;
+                lock (sessions)
+                {
+                    Session session = this.sessions[sessionID];
+                    session.Touch();
+                    return session;
+                }
             }
             else
             {
                 Session session = CreateSession();
-                this.sessions.Add(session.SessionID, session);
+                lock (this.sessions)
+                {
+                    this.sessions.Add(session.SessionID, session);
+                }
                 return session;
             }
         }