diff --git a/CHANGELOG.md b/CHANGELOG.md
index d0a64b4e7..f48638807 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -29,6 +29,7 @@ The following emojis are used to highlight certain changes:
 
 - 🛠 `boxo/gateway`: when making a trustless CAR request with the "entity-bytes" parameter, using a negative index greater than the underlying entity length could trigger reading more data than intended
 - 🛠 `boxo/gateway`: the header configuration `Config.Headers` and `AddAccessControlHeaders` has been replaced by the new middleware provided by `NewHeaders`.
+- 🛠 `routing/http/client`: the default HTTP client is no longer a global singleton. Therefore, using `WithUserAgent` won't modify the user agent of existing routing clients. This will also prevent potential race conditions. In addition, incompatible options will now return errors instead of silently failing.
 
 ### Security
 
diff --git a/routing/http/client/client.go b/routing/http/client/client.go
index efadc2732..16840cab5 100644
--- a/routing/http/client/client.go
+++ b/routing/http/client/client.go
@@ -28,15 +28,8 @@ import (
 )
 
 var (
-	_                 contentrouter.Client = &Client{}
-	logger                                 = logging.Logger("routing/http/client")
-	defaultHTTPClient                      = &http.Client{
-		Transport: &ResponseBodyLimitedTransport{
-			RoundTripper: http.DefaultTransport,
-			LimitBytes:   1 << 20,
-			UserAgent:    defaultUserAgent,
-		},
-	}
+	_      contentrouter.Client = &Client{}
+	logger                      = logging.Logger("routing/http/client")
 )
 
 const (
@@ -67,53 +60,75 @@ var defaultUserAgent = moduleVersion()
 
 var _ contentrouter.Client = &Client{}
 
+func newDefaultHTTPClient(userAgent string) *http.Client {
+	return &http.Client{
+		Transport: &ResponseBodyLimitedTransport{
+			RoundTripper: http.DefaultTransport,
+			LimitBytes:   1 << 20,
+			UserAgent:    userAgent,
+		},
+	}
+}
+
 type httpClient interface {
 	Do(req *http.Request) (*http.Response, error)
 }
 
-type Option func(*Client)
+type Option func(*Client) error
 
 func WithIdentity(identity crypto.PrivKey) Option {
-	return func(c *Client) {
+	return func(c *Client) error {
 		c.identity = identity
+		return nil
 	}
 }
 
+// WithHTTPClient sets a custom HTTP Client to be used with [Client].
 func WithHTTPClient(h httpClient) Option {
-	return func(c *Client) {
+	return func(c *Client) error {
 		c.httpClient = h
+		return nil
 	}
 }
 
+// WithUserAgent sets a custom user agent to use with the HTTP Client. This modifies
+// the underlying [http.Client]. Therefore, you should not use the same HTTP Client
+// with multiple routing clients.
+//
+// This only works if using a [http.Client] with a [ResponseBodyLimitedTransport]
+// set as its transport. Otherwise, an error will be returned.
 func WithUserAgent(ua string) Option {
-	return func(c *Client) {
+	return func(c *Client) error {
 		if ua == "" {
-			return
+			return errors.New("empty user agent")
 		}
 		httpClient, ok := c.httpClient.(*http.Client)
 		if !ok {
-			return
+			return errors.New("the http client of the Client must be a *http.Client")
 		}
 		transport, ok := httpClient.Transport.(*ResponseBodyLimitedTransport)
 		if !ok {
-			return
+			return errors.New("the transport of the http client of the Client must be a *ResponseBodyLimitedTransport")
 		}
 		transport.UserAgent = ua
+		return nil
 	}
 }
 
 func WithProviderInfo(peerID peer.ID, addrs []multiaddr.Multiaddr) Option {
-	return func(c *Client) {
+	return func(c *Client) error {
 		c.peerID = peerID
 		for _, a := range addrs {
 			c.addrs = append(c.addrs, types.Multiaddr{Multiaddr: a})
 		}
+		return nil
 	}
 }
 
 func WithStreamResultsRequired() Option {
-	return func(c *Client) {
+	return func(c *Client) error {
 		c.accepts = mediaTypeNDJSON
+		return nil
 	}
 }
 
@@ -122,13 +137,16 @@ func WithStreamResultsRequired() Option {
 func New(baseURL string, opts ...Option) (*Client, error) {
 	client := &Client{
 		baseURL:    baseURL,
-		httpClient: defaultHTTPClient,
+		httpClient: newDefaultHTTPClient(defaultUserAgent),
 		clock:      clock.New(),
 		accepts:    strings.Join([]string{mediaTypeNDJSON, mediaTypeJSON}, ","),
 	}
 
 	for _, opt := range opts {
-		opt(client)
+		err := opt(client)
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	if client.identity != nil && client.peerID.Size() != 0 && !client.peerID.MatchesPublicKey(client.identity.GetPublic()) {
diff --git a/routing/http/client/client_test.go b/routing/http/client/client_test.go
index 7edd77c10..590deed11 100644
--- a/routing/http/client/client_test.go
+++ b/routing/http/client/client_test.go
@@ -109,11 +109,10 @@ func makeTestDeps(t *testing.T, clientsOpts []Option, serverOpts []server.Option
 	server := httptest.NewServer(recordingHandler)
 	t.Cleanup(server.Close)
 	serverAddr := "http://" + server.Listener.Addr().String()
-	recordingHTTPClient := &recordingHTTPClient{httpClient: defaultHTTPClient}
+	recordingHTTPClient := &recordingHTTPClient{httpClient: newDefaultHTTPClient(testUserAgent)}
 	defaultClientOpts := []Option{
 		WithProviderInfo(peerID, addrs),
 		WithIdentity(identity),
-		WithUserAgent(testUserAgent),
 		WithHTTPClient(recordingHTTPClient),
 	}
 	c, err := New(serverAddr, append(defaultClientOpts, clientsOpts...)...)