diff --git a/js/data.go b/js/data.go
index ad62f3a8..6fe48f22 100644
--- a/js/data.go
+++ b/js/data.go
@@ -85,7 +85,7 @@ func atob(call otto.FunctionCall) otto.Value {
 
 	arg := argv[0]
 	if (!arg.IsString()) {
-		return ReportError("btoa: single argument must be a string.")
+		return ReportError("atob: single argument must be a string.")
 	}
 
 	decoded, err := base64.StdEncoding.DecodeString(arg.String())