1 files changed, 3 insertions, 1 deletions
diff --git a/runtime/js/30_fs.js b/runtime/js/30_fs.js
index bdd575f19..51f2c411e 100644
--- a/runtime/js/30_fs.js
+++ b/runtime/js/30_fs.js
@@ -5,7 +5,9 @@
   const core = window.Deno.core;
   const {
     Date,
+    DatePrototype,
     MathTrunc,
+    ObjectPrototypeIsPrototypeOf,
     SymbolAsyncIterator,
     SymbolIterator,
   } = window.__bootstrap.primordials;
@@ -277,7 +279,7 @@
   }
 
   function toUnixTimeFromEpoch(value) {
-    if (value instanceof Date) {
+    if (ObjectPrototypeIsPrototypeOf(DatePrototype, value)) {
       const time = value.valueOf();
       const seconds = MathTrunc(time / 1e3);
       const nanoseconds = MathTrunc(time - (seconds * 1e3)) * 1e6;