diff --git a/Sources/Environment.swift b/Sources/Environment.swift
index d220bf8..6b78fec 100644
--- a/Sources/Environment.swift
+++ b/Sources/Environment.swift
@@ -1,6 +1,6 @@
 public struct Environment {
   public let templateClass: Template.Type
-  public let extensions: [Extension]
+  public var extensions: [Extension]
 
   public var loader: Loader?