diff --git a/auth/oauth2adapt/oauth2adapt.go b/auth/oauth2adapt/oauth2adapt.go
index e266b0c9b158..9cc33e5ee648 100644
--- a/auth/oauth2adapt/oauth2adapt.go
+++ b/auth/oauth2adapt/oauth2adapt.go
@@ -100,8 +100,13 @@ func (ts *tokenSourceAdapter) Token() (*oauth2.Token, error) {
 		Expiry:      tok.Expiry,
 	}
 	// Preserve token metadata.
-	metadata := tok.Metadata
-	if metadata != nil {
+	m := tok.Metadata
+	if m != nil {
+		// Copy map to avoid concurrent map writes error (#11161).
+		metadata := make(map[string]interface{}, len(m)+2)
+		for k, v := range m {
+			metadata[k] = v
+		}
 		// Append compute token metadata in converted form.
 		if val, ok := metadata[authTokenSourceKey].(string); ok && val != "" {
 			metadata[oauth2TokenSourceKey] = val