diff --git a/genai/client.go b/genai/client.go
index fe9653f..7d0304d 100644
--- a/genai/client.go
+++ b/genai/client.go
@@ -75,10 +75,14 @@ Import the option package as "google.golang.org/api/option".`)
 	if err != nil {
 		return nil, fmt.Errorf("creating file client: %w", err)
 	}
-	cc, err := gl.NewCacheClient(ctx, opts...)
+
+	// Workaround for https://github.com/google/generative-ai-go/issues/151
+	optsForCache := removeHTTPClientOption(opts)
+	cc, err := gl.NewCacheClient(ctx, optsForCache...)
 	if err != nil {
 		return nil, fmt.Errorf("creating cache client: %w", err)
 	}
+
 	ds, err := gld.NewService(ctx, opts...)
 	if err != nil {
 		return nil, fmt.Errorf("creating discovery client: %w", err)
@@ -110,6 +114,19 @@ func hasAuthOption(opts []option.ClientOption) bool {
 	return false
 }
 
+// removeHTTPClientOption removes option.withHTTPClient from the given list
+// of options, if it exists; it returns the new (filtered) list.
+func removeHTTPClientOption(opts []option.ClientOption) []option.ClientOption {
+	var newOpts []option.ClientOption
+	for _, opt := range opts {
+		ts := reflect.ValueOf(opt).Type().String()
+		if ts != "option.withHTTPClient" {
+			newOpts = append(newOpts, opt)
+		}
+	}
+	return newOpts
+}
+
 // Close closes the client.
 func (c *Client) Close() error {
 	return errors.Join(c.gc.Close(), c.mc.Close(), c.fc.Close())
diff --git a/genai/client_test.go b/genai/client_test.go
index a3eb5a6..a6aca80 100644
--- a/genai/client_test.go
+++ b/genai/client_test.go
@@ -766,9 +766,33 @@ func TestRecoverPanic(t *testing.T) {
 	}
 }
 
+type customRT struct {
+	APIKey string
+}
+
+func (t *customRT) RoundTrip(req *http.Request) (*http.Response, error) {
+	transport := http.DefaultTransport.(*http.Transport).Clone()
+	newReq := req.Clone(req.Context())
+	vals := newReq.URL.Query()
+	vals.Set("key", t.APIKey)
+	newReq.URL.RawQuery = vals.Encode()
+
+	resp, err := transport.RoundTrip(newReq)
+	if err != nil {
+		return nil, err
+	}
+
+	return resp, nil
+}
+
 func TestCustomHTTPClient(t *testing.T) {
-	t.Skip("custom HTTP client not working right now")
-	c := http.DefaultClient
+	apiKey := os.Getenv("GEMINI_API_KEY")
+	if testing.Short() || apiKey == "" {
+		t.Skip("skipping live test in -short mode, or when API key isn't provided")
+	}
+	c := &http.Client{
+		Transport: &customRT{APIKey: apiKey},
+	}
 
 	ctx := context.Background()
 	client, err := NewClient(ctx, option.WithHTTPClient(c))
@@ -780,9 +804,10 @@ func TestCustomHTTPClient(t *testing.T) {
 	model := client.GenerativeModel(defaultModel)
 	resp, err := model.GenerateContent(ctx, Text("What are some of the largest cities in the US?"))
 	if err != nil {
-		log.Fatal(err)
+		t.Fatal(err)
 	}
-	fmt.Println(resp)
+	got := responseString(resp)
+	checkMatch(t, got, `new york`)
 }
 
 func uploadFile(t *testing.T, ctx context.Context, client *Client, filename string) *File {