diff --git a/lib/std/Thread.zig b/lib/std/Thread.zig
index aaf0fc34404200578b14c367bb4250ec82b021ae..d52515b88d06c4be90b285e994cbba48ab976bc9 100644
--- a/lib/std/Thread.zig
+++ b/lib/std/Thread.zig
@@ -513,7 +513,8 @@ const WindowsThreadImpl = struct {
         errdefer assert(windows.kernel32.HeapFree(heap_handle, 0, alloc_ptr) != 0);
 
         const instance_bytes = @ptrCast([*]u8, alloc_ptr)[0..alloc_bytes];
-        const instance = std.heap.FixedBufferAllocator.init(instance_bytes).allocator().create(Instance) catch unreachable;
+        var fba = std.heap.FixedBufferAllocator.init(instance_bytes);
+        const instance = fba.allocator().create(Instance) catch unreachable;
         instance.* = .{
             .fn_args = args,
             .thread = .{