diff --git a/lib/log.js b/lib/log.js
index f733971..f2e288b 100644
--- a/lib/log.js
+++ b/lib/log.js
@@ -19,7 +19,7 @@
       return "";
     } else if (o instanceof Uint8Array) {
       return new TextDecoder().decode(o);
-    } else if (Error.isError(o)) {
+    } else if (o instanceof Error) {
       return o.toString();
     } else {
       return "" + o;
diff --git a/src/log.iced b/src/log.iced
index f8e0cfb..5c00e46 100644
--- a/src/log.iced
+++ b/src/log.iced
@@ -20,7 +20,7 @@ default_level = L.INFO
 stringify = (o) ->
   if not o? then ""
   else if o instanceof Uint8Array then new TextDecoder().decode(o)
-  else if Error.isError(o) then o.toString()
+  else if o instanceof Error then o.toString()
   else ("" + o)
 
 ##=======================================================================
diff --git a/test/all.iced b/test/all.iced
index eb6f082..d98d514 100644
--- a/test/all.iced
+++ b/test/all.iced
@@ -70,7 +70,7 @@ class TestCase
   logger : () -> @_global.logger()
 
   search : (s, re, msg) ->
-    if Error.isError(s)
+    if s instanceof Error
       s = s.toString()
     @assert (s? and s.search(re) >= 0), msg