diff --git a/Tusker/LazilyDecoding.swift b/Tusker/LazilyDecoding.swift
index e96b4d7e..86cc4bf6 100644
--- a/Tusker/LazilyDecoding.swift
+++ b/Tusker/LazilyDecoding.swift
@@ -58,8 +58,8 @@ public struct LazilyDecoding<Enclosing, Value: Codable> {
 }
 
 extension LazilyDecoding {
-    init(arrayFrom keyPath: ReferenceWritableKeyPath<Enclosing, Data?>) {
-        self.init(from: keyPath, fallback: [] as! Value)
+    init<T: Codable>(arrayFrom keyPath: ReferenceWritableKeyPath<Enclosing, Data?>) where Value == [T] {
+        self.init(from: keyPath, fallback: [])
     }
 }