diff --git a/src/java/String.hxx b/src/java/String.hxx
index 715cf647b..d3aea4f73 100644
--- a/src/java/String.hxx
+++ b/src/java/String.hxx
@@ -67,7 +67,7 @@ public:
 	 * nullptr on error
 	 */
 	char *CopyTo(JNIEnv *env,
-		     char *buffer, size_t max_size) noexcept {
+		     char *buffer, size_t max_size) const noexcept {
 		return CopyTo(env, Get(), buffer, max_size);
 	}