diff --git a/lib/std/Thread.zig b/lib/std/Thread.zig
index 6be9f06f779bd88664e1b2a55e54c5a90dc06932..8f31add6e20892c48bf1872fc6829ca55a4bd357 100644
--- a/lib/std/Thread.zig
+++ b/lib/std/Thread.zig
@@ -1489,7 +1489,7 @@ const LinuxThreadImpl = struct {
         }
 
         // Prepare the TLS segment and prepare a user_desc struct when needed on x86
-        var tls_ptr = linux.tls.prepareArea(mapped[tls_offset..]);
+        var tls_ptr = linux.tls.prepareArea(mapped[tls_offset..][0..linux.tls.area_desc.size]);
         var user_desc: if (target.cpu.arch == .x86) linux.user_desc else void = undefined;
         if (target.cpu.arch == .x86) {
             defer tls_ptr = @intFromPtr(&user_desc);