diff --git a/lib/std/os.zig b/lib/std/os.zig
index 7a26126b1c36d0b85cfc1895e16d48e67df8a97d..899488456619c0d73cdd656f34433e7198dde9ba 100644
--- a/lib/std/os.zig
+++ b/lib/std/os.zig
@@ -2588,7 +2588,7 @@ pub fn isatty(handle: fd_t) bool {
             }
         }
     }
-    unreachable;
+    return system.isatty(handle) != 0;
 }
 
 pub fn isCygwinPty(handle: fd_t) bool {