diff --git a/src/Http/Authentication.Core/src/AuthenticationService.cs b/src/Http/Authentication.Core/src/AuthenticationService.cs
index 7efce69ce8..9cc0807539 100644
--- a/src/Http/Authentication.Core/src/AuthenticationService.cs
+++ b/src/Http/Authentication.Core/src/AuthenticationService.cs
@@ -253,7 +253,7 @@ namespace Microsoft.AspNetCore.Authentication
             var schemes = await GetAllSignInSchemeNames();
 
             // CookieAuth is the only implementation of sign-in.
-            var footer = $" Did you forget to call AddAuthentication().AddCookies(\"{scheme}\",...)?";
+            var footer = $" Did you forget to call AddAuthentication().AddCookie(\"{scheme}\",...)?";
 
             if (string.IsNullOrEmpty(schemes))
             {
@@ -275,7 +275,7 @@ namespace Microsoft.AspNetCore.Authentication
             {
                 // CookieAuth is the only implementation of sign-in.
                 return new InvalidOperationException(mismatchError
-                    + $"Did you forget to call AddAuthentication().AddCookies(\"Cookies\") and SignInAsync(\"Cookies\",...)?");
+                    + $"Did you forget to call AddAuthentication().AddCookie(\"Cookies\") and SignInAsync(\"Cookies\",...)?");
             }
 
             return new InvalidOperationException(mismatchError + $"The registered sign-in schemes are: {schemes}.");
@@ -292,7 +292,7 @@ namespace Microsoft.AspNetCore.Authentication
         {
             var schemes = await GetAllSignOutSchemeNames();
 
-            var footer = $" Did you forget to call AddAuthentication().AddCookies(\"{scheme}\",...)?";
+            var footer = $" Did you forget to call AddAuthentication().AddCookie(\"{scheme}\",...)?";
 
             if (string.IsNullOrEmpty(schemes))
             {
@@ -314,7 +314,7 @@ namespace Microsoft.AspNetCore.Authentication
             {
                 // CookieAuth is the most common implementation of sign-out, but OpenIdConnect and WsFederation also support it.
                 return new InvalidOperationException(mismatchError
-                    + $"Did you forget to call AddAuthentication().AddCookies(\"Cookies\") and {nameof(SignOutAsync)}(\"Cookies\",...)?");
+                    + $"Did you forget to call AddAuthentication().AddCookie(\"Cookies\") and {nameof(SignOutAsync)}(\"Cookies\",...)?");
             }
 
             return new InvalidOperationException(mismatchError + $"The registered sign-out schemes are: {schemes}.");