diff --git a/lib/compiler/build_runner.zig b/lib/compiler/build_runner.zig
index ea1cfda2668a514861d6a74a0572ff6a0bd8b90c..7cc3d2bcd7d03054d29f11d300ca64e4134e0fd7 100644
--- a/lib/compiler/build_runner.zig
+++ b/lib/compiler/build_runner.zig
@@ -682,9 +682,12 @@ fn runStepNames(
     }
 
     const ttyconf = run.ttyconf;
-    const stderr = run.stderr;
 
     if (run.summary != .none) {
+        std.debug.lockStdErr();
+        defer std.debug.unlockStdErr();
+        const stderr = run.stderr;
+
         const total_count = success_count + failure_count + pending_count + skipped_count;
         ttyconf.setColor(stderr, .cyan) catch {};
         stderr.writeAll("Build Summary:") catch {};