diff --git a/internal/client/repository/http/http_client.go b/internal/client/repository/http/http_client.go
index 8c73a29..e7f9b2d 100644
--- a/internal/client/repository/http/http_client.go
+++ b/internal/client/repository/http/http_client.go
@@ -3,6 +3,7 @@ package http
 import (
 	"context"
 	"fmt"
+	"net"
 
 	http "github.com/valyala/fasthttp"
 
@@ -33,6 +34,19 @@ func NewHTTPClientRepository(c *http.Client) client.Repository {
 }
 
 func (repo *httpClientRepository) Get(ctx context.Context, cid *domain.ClientID) (*domain.Client, error) {
+	ips, err := net.LookupIP(cid.URL().Hostname())
+	if err != nil {
+		return nil, fmt.Errorf("cannot resolve client IP by id: %w", err)
+	}
+
+	for _, ip := range ips {
+		if !ip.IsLoopback() {
+			continue
+		}
+
+		return nil, client.ErrNotExist
+	}
+
 	req := http.AcquireRequest()
 	defer http.ReleaseRequest(req)
 	req.SetRequestURI(cid.String())
diff --git a/internal/client/repository/memory/memory_client.go b/internal/client/repository/memory/memory_client.go
index 8f91db3..e4d433f 100644
--- a/internal/client/repository/memory/memory_client.go
+++ b/internal/client/repository/memory/memory_client.go
@@ -3,6 +3,7 @@ package memory
 import (
 	"context"
 	"fmt"
+	"net"
 	"path"
 	"sync"
 
@@ -29,6 +30,18 @@ func (repo *memoryClientRepository) Create(ctx context.Context, client *domain.C
 }
 
 func (repo *memoryClientRepository) Get(ctx context.Context, id *domain.ClientID) (*domain.Client, error) {
+	// WARN(toby3d): more often than not, we will work from tests with
+	// non-existent clients, almost guaranteed to cause a resolution error.
+	ips, _ := net.LookupIP(id.URL().Hostname())
+
+	for _, ip := range ips {
+		if !ip.IsLoopback() {
+			continue
+		}
+
+		return nil, client.ErrNotExist
+	}
+
 	src, ok := repo.store.Load(path.Join(DefaultPathPrefix, id.String()))
 	if !ok {
 		return nil, fmt.Errorf("cannot find client in store: %w", client.ErrNotExist)
diff --git a/internal/client/usecase/client_ucase_test.go b/internal/client/usecase/client_ucase_test.go
index 386fffb..ae263f7 100644
--- a/internal/client/usecase/client_ucase_test.go
+++ b/internal/client/usecase/client_ucase_test.go
@@ -2,11 +2,13 @@ package usecase_test
 
 import (
 	"context"
+	"errors"
 	"path"
 	"reflect"
 	"sync"
 	"testing"
 
+	"source.toby3d.me/toby3d/auth/internal/client"
 	repository "source.toby3d.me/toby3d/auth/internal/client/repository/memory"
 	"source.toby3d.me/toby3d/auth/internal/client/usecase"
 	"source.toby3d.me/toby3d/auth/internal/domain"
@@ -15,18 +17,48 @@ import (
 func TestDiscovery(t *testing.T) {
 	t.Parallel()
 
-	client := domain.TestClient(t)
-
 	store := new(sync.Map)
-	store.Store(path.Join(repository.DefaultPathPrefix, client.ID.String()), client)
+	testClient, localhostClient := domain.TestClient(t), domain.TestClient(t)
+	localhostClient.ID, _ = domain.ParseClientID("http://localhost/")
 
-	result, err := usecase.NewClientUseCase(repository.NewMemoryClientRepository(store)).
-		Discovery(context.Background(), client.ID)
-	if err != nil {
-		t.Fatal(err)
+	for _, client := range []*domain.Client{testClient, localhostClient} {
+		store.Store(path.Join(repository.DefaultPathPrefix, client.ID.String()), client)
 	}
 
-	if !reflect.DeepEqual(result, client) {
-		t.Errorf("Discovery(%s) = %+v, want %+v", client.ID, result, client)
+	for _, tc := range []struct {
+		name     string
+		in       *domain.Client
+		out      *domain.Client
+		expError error
+	}{{
+		name: "default",
+		in:   testClient,
+		out:  testClient,
+	}, {
+		name:     "localhost",
+		in:       localhostClient,
+		expError: client.ErrNotExist,
+	}} {
+		tc := tc
+
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			result, err := usecase.NewClientUseCase(repository.NewMemoryClientRepository(store)).
+				Discovery(context.Background(), tc.in.ID)
+			if tc.expError != nil && !errors.Is(err, tc.expError) {
+				t.Errorf("Discovery(%s) = %+v, want %+v", tc.in.ID, err, tc.expError)
+
+				return
+			}
+
+			if tc.expError == nil && err != nil {
+				t.Fatal(err)
+			}
+
+			if !reflect.DeepEqual(result, tc.out) {
+				t.Errorf("Discovery(%s) = %+v, want %+v", tc.in.ID, result, tc.out)
+			}
+		})
 	}
 }
diff --git a/internal/domain/client_id.go b/internal/domain/client_id.go
index 4b41165..8bc5179 100644
--- a/internal/domain/client_id.go
+++ b/internal/domain/client_id.go
@@ -107,7 +107,7 @@ func ParseClientID(src string) (*ClientID, error) {
 func TestClientID(tb testing.TB) *ClientID {
 	tb.Helper()
 
-	clientID, err := ParseClientID("https://indieauth.example.com/")
+	clientID, err := ParseClientID("https://example.com/")
 	if err != nil {
 		tb.Fatal(err)
 	}