diff --git a/IntegrationTests/TestSuites/Sources/ConcurrencyTests/main.swift b/IntegrationTests/TestSuites/Sources/ConcurrencyTests/main.swift
index c80e4877..96c2711b 100644
--- a/IntegrationTests/TestSuites/Sources/ConcurrencyTests/main.swift
+++ b/IntegrationTests/TestSuites/Sources/ConcurrencyTests/main.swift
@@ -9,7 +9,7 @@ import Darwin
 #if compiler(>=5.5)
 
 func performanceNow() -> Double {
-    return JSObject.global.performance.now.function!().number!
+    return JSObject.global.performance.now().number!
 }
 
 func measure(_ block: () async throws -> Void) async rethrows -> Double {
diff --git a/IntegrationTests/lib.js b/IntegrationTests/lib.js
index e708816c..1d7b6342 100644
--- a/IntegrationTests/lib.js
+++ b/IntegrationTests/lib.js
@@ -64,6 +64,7 @@ const WASI = {
             args: [programName],
             env: {},
             returnOnExit: false,
+            version: "preview1",
         })
 
         return {