diff --git a/shared/AppInsightsCore/Tests/Unit/src/ApplicationInsightsCore.Tests.ts b/shared/AppInsightsCore/Tests/Unit/src/ApplicationInsightsCore.Tests.ts
index e11aae210..04743ad3c 100644
--- a/shared/AppInsightsCore/Tests/Unit/src/ApplicationInsightsCore.Tests.ts
+++ b/shared/AppInsightsCore/Tests/Unit/src/ApplicationInsightsCore.Tests.ts
@@ -256,6 +256,25 @@ export class ApplicationInsightsCoreTests extends AITestClass {
             }
         });
 
+        this.testCase({
+            name: "ApplicationInsightsCore: PerfMgr should be created as expected",
+            test: () => {
+                let channelPlugin = new TestChannelPlugin();
+                const appInsightsCore = new AppInsightsCore();
+                appInsightsCore.initialize(
+                    { 
+                        instrumentationKey: "testIkey", 
+                        channels: [[channelPlugin]],
+                        enablePerfMgr: true
+                    } as IConfiguration,
+                        
+                    []);
+                let perfMgr = appInsightsCore.getPerfMgr();
+                Assert.ok(perfMgr, "perfMgr should be created without customized createPerfMgr function");
+            }
+        });
+
+
 
         this.testCase({
             name: "ApplicationInsightsCore: Initialization initializes setNextPlugin",
diff --git a/shared/AppInsightsCore/src/JavaScriptSDK/AppInsightsCore.ts b/shared/AppInsightsCore/src/JavaScriptSDK/AppInsightsCore.ts
index bf778af42..008fbf7b7 100644
--- a/shared/AppInsightsCore/src/JavaScriptSDK/AppInsightsCore.ts
+++ b/shared/AppInsightsCore/src/JavaScriptSDK/AppInsightsCore.ts
@@ -1299,7 +1299,9 @@ export class AppInsightsCore<CfgType extends IConfiguration = IConfiguration> im
                     let enablePerfMgr = details.cfg.enablePerfMgr;
                     if (enablePerfMgr) {
                         let createPerfMgr = details.cfg.createPerfMgr;
-                        if (prevCfgPerfMgr !== createPerfMgr) {
+                        // for preCfgPerfMgr = createPerfMgr = null
+                        // initial createPerfMgr function should be _createPerfManager
+                        if ((prevCfgPerfMgr !== createPerfMgr) || !prevCfgPerfMgr) {
                             if (!createPerfMgr) {
                                 createPerfMgr = _createPerfManager;
                             }