diff --git a/Foundation/URLSession/URLSession.swift b/Foundation/URLSession/URLSession.swift
index 3a07673328..7690cc42b9 100644
--- a/Foundation/URLSession/URLSession.swift
+++ b/Foundation/URLSession/URLSession.swift
@@ -406,9 +406,11 @@ extension URLSession._Request {
 
 fileprivate extension URLSession {
     func createNextTaskIdentifier() -> Int {
-        let i = nextTaskIdentifier
-        nextTaskIdentifier += 1
-        return i
+        return workQueue.sync {
+            let i = nextTaskIdentifier
+            nextTaskIdentifier += 1
+            return i
+        }
     }
 }