diff --git a/src/Microsoft.Identity.Web/WebApiExtensions/MicrosoftIdentityWebApiAuthenticationBuilderExtensions.cs b/src/Microsoft.Identity.Web/WebApiExtensions/MicrosoftIdentityWebApiAuthenticationBuilderExtensions.cs
index 875b25099..ea3b8056e 100644
--- a/src/Microsoft.Identity.Web/WebApiExtensions/MicrosoftIdentityWebApiAuthenticationBuilderExtensions.cs
+++ b/src/Microsoft.Identity.Web/WebApiExtensions/MicrosoftIdentityWebApiAuthenticationBuilderExtensions.cs
@@ -230,7 +230,7 @@ private static void AddMicrosoftIdentityWebApiImplementation(
                     }
 
                     options.TokenValidationParameters.EnableAadSigningKeyIssuerValidation();
-                    options.Events.OnMessageReceived = async context =>
+                    options.Events.OnMessageReceived += async context =>
                     {
                         context.Options.TokenValidationParameters.ConfigurationManager ??= options.ConfigurationManager as BaseConfigurationManager;
                         await Task.CompletedTask.ConfigureAwait(false);