diff --git a/lib/std/Io/Threaded.zig b/lib/std/Io/Threaded.zig
index b6ba5f9a8209e6b825320e8e01ecc764e19d7ce9..999d7b93f503729e0f83f4c890ce6d809da5b21d 100644
--- a/lib/std/Io/Threaded.zig
+++ b/lib/std/Io/Threaded.zig
@@ -490,7 +490,7 @@ fn async(
     start: *const fn (context: *const anyopaque, result: *anyopaque) void,
 ) ?*Io.AnyFuture {
     const t: *Threaded = @ptrCast(@alignCast(userdata));
-    if (t.cpu_count == 1) {
+    if (t.cpu_count == 1 or builtin.single_threaded) {
         start(context.ptr, result.ptr);
         return null;
     }