diff --git a/lib/compiler/test_runner.zig b/lib/compiler/test_runner.zig
index b0ef17a7e9..f7f59a5bf3 100644
--- a/lib/compiler/test_runner.zig
+++ b/lib/compiler/test_runner.zig
@@ -405,15 +405,22 @@ pub fn fuzz(
             testOne(ctx, input.toSlice()) catch |err| switch (err) {
                 error.SkipZigTest => return,
                 else => {
-                    std.debug.lockStdErr();
-                    if (@errorReturnTrace()) |trace| std.debug.dumpStackTrace(trace);
-                    std.debug.print("failed with error.{t}\n", .{err});
+                    const stderr = std.debug.lockStderrWriter(&.{});
+                    p: {
+                        if (@errorReturnTrace()) |trace| {
+                            std.debug.writeStackTrace(trace, &stderr.interface, stderr.mode) catch break :p;
+                        }
+                        stderr.interface.print("failed with error.{t}\n", .{err}) catch break :p;
+                        stderr.interface.flush() catch break :p;
+                    }
+                    stderr.interface.flush() catch {};
                     std.process.exit(1);
                 },
             };
             if (log_err_count != 0) {
-                std.debug.lockStdErr();
-                std.debug.print("error logs detected\n", .{});
+                const stderr = std.debug.lockStderrWriter(&.{});
+                stderr.interface.print("error logs detected\n", .{}) catch {};
+                stderr.interface.flush() catch {};
                 std.process.exit(1);
             }
         }
diff --git a/lib/std/debug/simple_panic.zig b/lib/std/debug/simple_panic.zig
index f6ff77e04f..2d0e5abf4e 100644
--- a/lib/std/debug/simple_panic.zig
+++ b/lib/std/debug/simple_panic.zig
@@ -14,9 +14,9 @@ const std = @import("../std.zig");
 pub fn call(msg: []const u8, ra: ?usize) noreturn {
     @branchHint(.cold);
     _ = ra;
-    std.debug.lockStdErr();
-    const stderr: std.Io.File = .stderr();
-    stderr.writeAll(msg) catch {};
+    const stderr = std.debug.lockStderrWriter(&.{});
+    stderr.interface.writeAll(msg) catch {};
+    stderr.interface.flush(msg) catch {};
     @trap();
 }
 
diff --git a/lib/std/process.zig b/lib/std/process.zig
index 5c6e6f89eb..216e793cbe 100644
--- a/lib/std/process.zig
+++ b/lib/std/process.zig
@@ -1841,21 +1841,19 @@ pub fn totalSystemMemory() TotalSystemMemoryError!u64 {
     }
 }
 
-/// Indicate that we are now terminating with a successful exit code.
-/// In debug builds, this is a no-op, so that the calling code's
-/// cleanup mechanisms are tested and so that external tools that
-/// check for resource leaks can be accurate. In release builds, this
-/// calls exit(0), and does not return.
-pub fn cleanExit() void {
-    if (builtin.mode == .Debug) {
-        return;
-    } else {
-        std.debug.lockStdErr();
-        exit(0);
-    }
+/// Indicate intent to terminate with a successful exit code.
+///
+/// In debug builds, this is a no-op, so that the calling code's cleanup
+/// mechanisms are tested and so that external tools checking for resource
+/// leaks can be accurate. In release builds, this calls `exit` with code zero,
+/// and does not return.
+pub fn cleanExit(io: Io) void {
+    if (builtin.mode == .Debug) return;
+    _ = io.lockStderrWriter(&.{});
+    exit(0);
 }
 
-/// Raise the open file descriptor limit.
+/// Request ability to have more open file descriptors simultaneously.
 ///
 /// On some systems, this raises the limit before seeing ProcessFdQuotaExceeded
 /// errors. On other systems, this does nothing.
diff --git a/src/main.zig b/src/main.zig
index c1f5e3c026..160b9919eb 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -4429,12 +4429,12 @@ fn runOrTest(
     // the error message and invocation below.
     if (process.can_execv and arg_mode == .run) {
         // execv releases the locks; no need to destroy the Compilation here.
-        std.debug.lockStdErr();
+        _ = std.debug.lockStderrWriter(&.{});
         const err = process.execve(gpa, argv.items, &env_map);
-        std.debug.unlockStdErr();
+        std.debug.unlockStderrWriter();
         try warnAboutForeignBinaries(io, arena, arg_mode, target, link_libc);
         const cmd = try std.mem.join(arena, " ", argv.items);
-        fatal("the following command failed to execve with '{s}':\n{s}", .{ @errorName(err), cmd });
+        fatal("the following command failed to execve with '{t}':\n{s}", .{ err, cmd });
     } else if (process.can_spawn) {
         var child = std.process.Child.init(argv.items, gpa);
         child.env_map = &env_map;
@@ -4448,8 +4448,8 @@ fn runOrTest(
         comp_destroyed.* = true;
 
         const term_result = t: {
-            std.debug.lockStdErr();
-            defer std.debug.unlockStdErr();
+            _ = std.debug.lockStderrWriter();
+            defer std.debug.unlockStderrWriter();
             break :t child.spawnAndWait(io);
         };
         const term = term_result catch |err| {