diff --git a/test/standalone/build.zig b/test/standalone/build.zig
index e2b7a7c387..033f350a0e 100644
--- a/test/standalone/build.zig
+++ b/test/standalone/build.zig
@@ -42,6 +42,7 @@ pub fn build(b: *std.Build) void {
         "../../tools/update-linux-headers.zig",
         "../../tools/update_clang_options.zig",
         "../../tools/update_cpu_features.zig",
+        "../../tools/update_freebsd_libc.zig",
         "../../tools/update_glibc.zig",
     }) |tool_src_path| {
         const tool = b.addTest(.{
diff --git a/tools/update_freebsd_libc.zig b/tools/update_freebsd_libc.zig
new file mode 100644
index 0000000000..420147e0df
--- /dev/null
+++ b/tools/update_freebsd_libc.zig
@@ -0,0 +1,65 @@
+//! This script updates the .c, .h, .s, and .S files that make up the start
+//! files such as crt1.o.
+//!
+//! Example usage:
+//! `zig run tools/update_freebsd_libc.zig -- ~/Downloads/freebsd-src .`
+
+const std = @import("std");
+
+const exempt_files = [_][]const u8{
+    // This file is maintained by a separate project and does not come from FreeBSD.
+    "abilists",
+};
+
+pub fn main() !void {
+    var arena_instance = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    defer arena_instance.deinit();
+    const arena = arena_instance.allocator();
+
+    const args = try std.process.argsAlloc(arena);
+    const freebsd_src_path = args[1];
+    const zig_src_path = args[2];
+
+    const dest_dir_path = try std.fmt.allocPrint(arena, "{s}/lib/libc/freebsd", .{zig_src_path});
+
+    var dest_dir = std.fs.cwd().openDir(dest_dir_path, .{ .iterate = true }) catch |err| {
+        std.log.err("unable to open destination directory '{s}': {s}", .{
+            dest_dir_path, @errorName(err),
+        });
+        std.process.exit(1);
+    };
+    defer dest_dir.close();
+
+    var freebsd_src_dir = try std.fs.cwd().openDir(freebsd_src_path, .{});
+    defer freebsd_src_dir.close();
+
+    // Copy updated files from upstream.
+    {
+        var walker = try dest_dir.walk(arena);
+        defer walker.deinit();
+
+        walk: while (try walker.next()) |entry| {
+            if (entry.kind != .file) continue;
+            if (std.mem.startsWith(u8, entry.basename, ".")) continue;
+            for (exempt_files) |p| {
+                if (std.mem.eql(u8, entry.path, p)) continue :walk;
+            }
+
+            std.log.info("updating '{s}/{s}' from '{s}/{s}'", .{
+                dest_dir_path,    entry.path,
+                freebsd_src_path, entry.path,
+            });
+
+            freebsd_src_dir.copyFile(entry.path, dest_dir, entry.path, .{}) catch |err| {
+                std.log.warn("unable to copy '{s}/{s}' to '{s}/{s}': {s}", .{
+                    freebsd_src_path, entry.path,
+                    dest_dir_path,    entry.path,
+                    @errorName(err),
+                });
+                if (err == error.FileNotFound) {
+                    try dest_dir.deleteFile(entry.path);
+                }
+            };
+        }
+    }
+}