diff --git a/auth/token_generator.go b/auth/token_generator.go
index ddf777be..7aa2d564 100644
--- a/auth/token_generator.go
+++ b/auth/token_generator.go
@@ -172,12 +172,12 @@ type iamSigner struct {
 
 func newIAMSigner(ctx context.Context, config *internal.AuthConfig) (*iamSigner, error) {
 	hc, _, err := internal.NewHTTPClient(ctx, config.Opts...)
-	hc.Opts = []internal.HTTPOption{
-		internal.WithHeader("x-goog-api-client", internal.GetMetricsHeader(config.Version)),
-	}
 	if err != nil {
 		return nil, err
 	}
+	hc.Opts = []internal.HTTPOption{
+		internal.WithHeader("x-goog-api-client", internal.GetMetricsHeader(config.Version)),
+	}
 
 	return &iamSigner{
 		mutex:        &sync.Mutex{},
diff --git a/iid/iid.go b/iid/iid.go
index 259f3c36..7a3e9b55 100644
--- a/iid/iid.go
+++ b/iid/iid.go
@@ -116,12 +116,12 @@ func NewClient(ctx context.Context, c *internal.InstanceIDConfig) (*Client, erro
 	}
 
 	hc, _, err := internal.NewHTTPClient(ctx, c.Opts...)
-	hc.Opts = []internal.HTTPOption{
-		internal.WithHeader("x-goog-api-client", internal.GetMetricsHeader(c.Version)),
-	}
 	if err != nil {
 		return nil, err
 	}
+	hc.Opts = []internal.HTTPOption{
+		internal.WithHeader("x-goog-api-client", internal.GetMetricsHeader(c.Version)),
+	}
 
 	hc.CreateErrFn = createError
 	return &Client{
diff --git a/internal/http_client.go b/internal/http_client.go
index 9adffefd..9463f98e 100644
--- a/internal/http_client.go
+++ b/internal/http_client.go
@@ -444,6 +444,7 @@ func retryNetworkAndHTTPErrors(statusCodes ...int) RetryCondition {
 	}
 }
 
+// GetMetricsHeader constructs header value for metrics attribution
 func GetMetricsHeader(sdkVersion string) string {
 	goVersion := strings.TrimPrefix(runtime.Version(), "go")
 	return fmt.Sprintf("gl-go/%s fire-admin/%s", goVersion, sdkVersion)