only decode as map if plain object

1 files changed, 7 insertions, 7 deletions

diff --git a/src/gleam_stdlib.mjs b/src/gleam_stdlib.mjs
index 4f54c4d..1fa2563 100644
--- a/src/gleam_stdlib.mjs
+++ b/src/gleam_stdlib.mjs
@@ -673,14 +673,14 @@ export function decode_result(data) {
   return Result.isResult(data) ? new Ok(data) : decoder_error("Result", data);
 }
 
-function decode_object_to_map(data) {
-  return typeof data === 'object' && data !== null && !Array.isArray(data)
-    ? new Ok(new Map(Object.entries(data)))
-    : decoder_error("Map", data);
-}
-
 export function decode_map(data) {
-  return data instanceof Map ? new Ok(data) : decode_object_to_map(data);
+  if (data instanceof Map) {
+    return new Ok(data)
+  }
+  if (typeof data === 'object' && data !== null && Object.getPrototypeOf(data) == Object.getPrototypeOf({})) {
+    return new Ok(new Map(Object.entries(data)))
+  }
+  return  decoder_error("Map", data);
 }
 
 export function decode_option(data, decoder) {