diff --git a/src/OpenIddict.Validation/OpenIddictValidationHandlers.Introspection.cs b/src/OpenIddict.Validation/OpenIddictValidationHandlers.Introspection.cs
index 3288aa72..150699cb 100644
--- a/src/OpenIddict.Validation/OpenIddictValidationHandlers.Introspection.cs
+++ b/src/OpenIddict.Validation/OpenIddictValidationHandlers.Introspection.cs
@@ -27,7 +27,7 @@ namespace OpenIddict.Validation
                  * Introspection response handling:
                  */
                 AttachCredentials.Descriptor,
-                AttachAccessToken.Descriptor,
+                AttachToken.Descriptor,
 
                 /*
                  * Introspection response handling:
@@ -75,16 +75,16 @@ namespace OpenIddict.Validation
             }
 
             /// <summary>
-            /// Contains the logic responsible of attaching the access token to the introspection request.
+            /// Contains the logic responsible of attaching the token to the introspection request.
             /// </summary>
-            public class AttachAccessToken : IOpenIddictValidationHandler<PrepareIntrospectionRequestContext>
+            public class AttachToken : IOpenIddictValidationHandler<PrepareIntrospectionRequestContext>
             {
                 /// <summary>
                 /// Gets the default descriptor definition assigned to this handler.
                 /// </summary>
                 public static OpenIddictValidationHandlerDescriptor Descriptor { get; }
                     = OpenIddictValidationHandlerDescriptor.CreateBuilder<PrepareIntrospectionRequestContext>()
-                        .UseSingletonHandler<AttachAccessToken>()
+                        .UseSingletonHandler<AttachToken>()
                         .SetOrder(AttachCredentials.Descriptor.Order + 100_000)
                         .Build();
 
@@ -372,15 +372,19 @@ namespace OpenIddict.Validation
 
                     // OpenIddict-based authorization servers always return the actual token type using
                     // the special "token_usage" claim, that helps resource servers determine whether the
-                    // introspected token is an access token and thus prevent token substitution attacks.
-                    var usage = (string) context.Response[Claims.TokenUsage];
-                    if (!string.IsNullOrEmpty(usage) && !string.Equals(usage, context.TokenType, StringComparison.OrdinalIgnoreCase))
+                    // introspected token is of the expected type and prevent token substitution attacks.
+                    if (!string.IsNullOrEmpty(context.TokenType))
                     {
-                        context.Reject(
-                            error: Errors.InvalidToken,
-                            description: "The introspected token is not an access token.");
+                        var usage = (string) context.Response[Claims.TokenUsage];
+                        if (!string.IsNullOrEmpty(usage) &&
+                            !string.Equals(usage, context.TokenType, StringComparison.OrdinalIgnoreCase))
+                        {
+                            context.Reject(
+                                error: Errors.InvalidToken,
+                                description: "The type of the introspection token doesn't match the expected type.");
 
-                        return default;
+                            return default;
+                        }
                     }
 
                     return default;
diff --git a/src/OpenIddict.Validation/OpenIddictValidationService.cs b/src/OpenIddict.Validation/OpenIddictValidationService.cs
index c9756c38..ddf248d5 100644
--- a/src/OpenIddict.Validation/OpenIddictValidationService.cs
+++ b/src/OpenIddict.Validation/OpenIddictValidationService.cs
@@ -90,7 +90,9 @@ namespace OpenIddict.Validation
                         var message = new StringBuilder()
                             .AppendLine("An error occurred while preparing the configuration request.")
                             .AppendFormat("Error: {0}", context.Error ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error description: {0}", context.ErrorDescription ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error URI: {0}", context.ErrorUri ?? "(not available)")
                             .ToString();
 
@@ -115,7 +117,9 @@ namespace OpenIddict.Validation
                         var message = new StringBuilder()
                             .AppendLine("An error occurred while sending the configuration request.")
                             .AppendFormat("Error: {0}", context.Error ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error description: {0}", context.ErrorDescription ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error URI: {0}", context.ErrorUri ?? "(not available)")
                             .ToString();
 
@@ -140,7 +144,9 @@ namespace OpenIddict.Validation
                         var message = new StringBuilder()
                             .AppendLine("An error occurred while extracting the configuration response.")
                             .AppendFormat("Error: {0}", context.Error ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error description: {0}", context.ErrorDescription ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error URI: {0}", context.ErrorUri ?? "(not available)")
                             .ToString();
 
@@ -166,7 +172,9 @@ namespace OpenIddict.Validation
                         var message = new StringBuilder()
                             .AppendLine("An error occurred while handling the configuration response.")
                             .AppendFormat("Error: {0}", context.Error ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error description: {0}", context.ErrorDescription ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error URI: {0}", context.ErrorUri ?? "(not available)")
                             .ToString();
 
@@ -254,7 +262,9 @@ namespace OpenIddict.Validation
                         var message = new StringBuilder()
                             .AppendLine("An error occurred while preparing the cryptography request.")
                             .AppendFormat("Error: {0}", context.Error ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error description: {0}", context.ErrorDescription ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error URI: {0}", context.ErrorUri ?? "(not available)")
                             .ToString();
 
@@ -279,7 +289,9 @@ namespace OpenIddict.Validation
                         var message = new StringBuilder()
                             .AppendLine("An error occurred while sending the cryptography request.")
                             .AppendFormat("Error: {0}", context.Error ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error description: {0}", context.ErrorDescription ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error URI: {0}", context.ErrorUri ?? "(not available)")
                             .ToString();
 
@@ -304,7 +316,9 @@ namespace OpenIddict.Validation
                         var message = new StringBuilder()
                             .AppendLine("An error occurred while extracting the cryptography response.")
                             .AppendFormat("Error: {0}", context.Error ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error description: {0}", context.ErrorDescription ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error URI: {0}", context.ErrorUri ?? "(not available)")
                             .ToString();
 
@@ -330,7 +344,9 @@ namespace OpenIddict.Validation
                         var message = new StringBuilder()
                             .AppendLine("An error occurred while handling the cryptography response.")
                             .AppendFormat("Error: {0}", context.Error ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error description: {0}", context.ErrorDescription ?? "(not available)")
+                            .AppendLine()
                             .AppendFormat("Error URI: {0}", context.ErrorUri ?? "(not available)")
                             .ToString();
 
@@ -433,6 +449,21 @@ namespace OpenIddict.Validation
 
                     await provider.DispatchAsync(context);
 
+                    if (context.IsRejected)
+                    {
+                        var message = new StringBuilder()
+                            .AppendLine("An error occurred while preparing the introspection request.")
+                            .AppendFormat("Error: {0}", context.Error ?? "(not available)")
+                            .AppendLine()
+                            .AppendFormat("Error description: {0}", context.ErrorDescription ?? "(not available)")
+                            .AppendLine()
+                            .AppendFormat("Error URI: {0}", context.ErrorUri ?? "(not available)")
+                            .ToString();
+
+                        throw new OpenIddictExceptions.GenericException(message,
+                            context.Error, context.ErrorDescription, context.ErrorUri);
+                    }
+
                     return context.Request;
                 }
 
@@ -445,6 +476,21 @@ namespace OpenIddict.Validation
 
                     await provider.DispatchAsync(context);
 
+                    if (context.IsRejected)
+                    {
+                        var message = new StringBuilder()
+                            .AppendLine("An error occurred while sending the introspection request.")
+                            .AppendFormat("Error: {0}", context.Error ?? "(not available)")
+                            .AppendLine()
+                            .AppendFormat("Error description: {0}", context.ErrorDescription ?? "(not available)")
+                            .AppendLine()
+                            .AppendFormat("Error URI: {0}", context.ErrorUri ?? "(not available)")
+                            .ToString();
+
+                        throw new OpenIddictExceptions.GenericException(message,
+                            context.Error, context.ErrorDescription, context.ErrorUri);
+                    }
+
                     return context.Request;
                 }
 
@@ -457,6 +503,21 @@ namespace OpenIddict.Validation
 
                     await provider.DispatchAsync(context);
 
+                    if (context.IsRejected)
+                    {
+                        var message = new StringBuilder()
+                            .AppendLine("An error occurred while extracting the introspection response.")
+                            .AppendFormat("Error: {0}", context.Error ?? "(not available)")
+                            .AppendLine()
+                            .AppendFormat("Error description: {0}", context.ErrorDescription ?? "(not available)")
+                            .AppendLine()
+                            .AppendFormat("Error URI: {0}", context.ErrorUri ?? "(not available)")
+                            .ToString();
+
+                        throw new OpenIddictExceptions.GenericException(message,
+                            context.Error, context.ErrorDescription, context.ErrorUri);
+                    }
+
                     return context.Response;
                 }
 
@@ -472,6 +533,21 @@ namespace OpenIddict.Validation
 
                     await provider.DispatchAsync(context);
 
+                    if (context.IsRejected)
+                    {
+                        var message = new StringBuilder()
+                            .AppendLine("An error occurred while handling the introspection response.")
+                            .AppendFormat("Error: {0}", context.Error ?? "(not available)")
+                            .AppendLine()
+                            .AppendFormat("Error description: {0}", context.ErrorDescription ?? "(not available)")
+                            .AppendLine()
+                            .AppendFormat("Error URI: {0}", context.ErrorUri ?? "(not available)")
+                            .ToString();
+
+                        throw new OpenIddictExceptions.GenericException(message,
+                            context.Error, context.ErrorDescription, context.ErrorUri);
+                    }
+
                     return context.Principal;
                 }
             }