diff --git a/Upsilon/StandardLibraries/StaticScope.cs b/Upsilon/StandardLibraries/StaticScope.cs
index d38f7c2..1e7706e 100644
--- a/Upsilon/StandardLibraries/StaticScope.cs
+++ b/Upsilon/StandardLibraries/StaticScope.cs
@@ -27,11 +27,13 @@ namespace Upsilon.StandardLibraries
             {
                 if (_staticScope != null)
                     return _staticScope;
-
-                var (evaluationScope, boundScope) = CreateStandardLibrary();
-                _staticScope                      = evaluationScope;
-                _staticBoundScope                 = boundScope;
-                return _staticScope;
+                lock (Scope)
+                {
+                    var (evaluationScope, boundScope) = CreateStandardLibrary();
+                    _staticScope                      = evaluationScope;
+                    _staticBoundScope                 = boundScope;
+                    return _staticScope;
+                }
             }
         }