diff --git a/Package.swift b/Package.swift
index 1de099870c..34d030e3a4 100644
--- a/Package.swift
+++ b/Package.swift
@@ -1,4 +1,4 @@
-// swift-tools-version:4.0
+// swift-tools-version:5.0
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
 import PackageDescription
diff --git a/Sources/Apollo/InMemoryNormalizedCache.swift b/Sources/Apollo/InMemoryNormalizedCache.swift
index 0e0d948c7a..3c19fce743 100644
--- a/Sources/Apollo/InMemoryNormalizedCache.swift
+++ b/Sources/Apollo/InMemoryNormalizedCache.swift
@@ -1,3 +1,5 @@
+import Foundation
+
 public final class InMemoryNormalizedCache: NormalizedCache {
   private var records: RecordSet
 
diff --git a/Sources/Apollo/NormalizedCache.swift b/Sources/Apollo/NormalizedCache.swift
index 98d68309a6..cc338c36d7 100644
--- a/Sources/Apollo/NormalizedCache.swift
+++ b/Sources/Apollo/NormalizedCache.swift
@@ -1,3 +1,5 @@
+import Foundation
+
 public protocol NormalizedCache {
   
   /// Loads records corresponding to the given keys.