diff --git a/ext/json/fbuffer/fbuffer.h b/ext/json/fbuffer/fbuffer.h
index 1e860eb790..5a0a27cda5 100644
--- a/ext/json/fbuffer/fbuffer.h
+++ b/ext/json/fbuffer/fbuffer.h
@@ -181,7 +181,7 @@ static FBuffer *fbuffer_dup(FBuffer *fb)
 
 static VALUE fbuffer_to_s(FBuffer *fb)
 {
-    VALUE result = rb_str_new(FBUFFER_PAIR(fb));
+    VALUE result = rb_str_new(FBUFFER_PTR(fb), FBUFFER_LEN(fb));
     fbuffer_free(fb);
     FORCE_UTF8(result);
     return result;