diff --git a/src/main_wpt.zig b/src/main_wpt.zig
index 5237c197..eeabaf12 100644
--- a/src/main_wpt.zig
+++ b/src/main_wpt.zig
@@ -138,8 +138,9 @@ pub fn main() !void {
         var arena = std.heap.ArenaAllocator.init(alloc);
         defer arena.deinit();
 
-        const res = wpt.run(arena.allocator(), wpt_dir, tc, &loader) catch |err| {
-            const suite = try Suite.init(alloc, tc, false, @errorName(err));
+        var msg_out: ?[]const u8 = null;
+        const res = wpt.run(arena.allocator(), wpt_dir, tc, &loader, &msg_out) catch |err| {
+            const suite = try Suite.init(alloc, tc, false, if (msg_out) |msg| msg else @errorName(err));
             try results.append(suite);
 
             if (out == .text) {
diff --git a/src/wpt/run.zig b/src/wpt/run.zig
index 5c7c6d15..27dc28c8 100644
--- a/src/wpt/run.zig
+++ b/src/wpt/run.zig
@@ -30,7 +30,7 @@ const polyfill = @import("../browser/polyfill/polyfill.zig");
 // runWPT parses the given HTML file, starts a js env and run the first script
 // tags containing javascript sources.
 // It loads first the js libs files.
-pub fn run(arena: Allocator, comptime dir: []const u8, f: []const u8, loader: *FileLoader) ![]const u8 {
+pub fn run(arena: Allocator, comptime dir: []const u8, f: []const u8, loader: *FileLoader, msg_out: *?[]const u8) ![]const u8 {
     // document
     const html = blk: {
         const file = try std.fs.cwd().openFile(f, .{});
@@ -98,7 +98,17 @@ pub fn run(arena: Allocator, comptime dir: []const u8, f: []const u8, loader: *F
     );
 
     // wait for all async executions
-    try runner.loop.run();
+    {
+        var try_catch: Env.TryCatch = undefined;
+        try_catch.init(runner.executor);
+        defer try_catch.deinit();
+        runner.loop.run() catch |err| {
+            if (try try_catch.err(arena)) |msg| {
+                msg_out.* = msg;
+            }
+            return err;
+        };
+    }
 
     // Check the final test status.
     try runner.exec("report.status;");