diff --git a/src/ArenaAllocator.zig b/src/ArenaAllocator.zig
index 2ccb08d19aea53..c2d8718fd4d3a7 100644
--- a/src/ArenaAllocator.zig
+++ b/src/ArenaAllocator.zig
@@ -1,4 +1,3 @@
-/// TODO: delete this once we've upgraded Zig and https://github.com/ziglang/zig/pull/15985 is merged.
 const std = @import("std");
 const assert = std.debug.assert;
 const mem = std.mem;
@@ -152,7 +151,7 @@ pub const ArenaAllocator = struct {
                     return false;
                 };
                 self.child_allocator.rawFree(first_alloc_buf, align_bits, @returnAddress());
-                const node = @as(*BufNode, @ptrCast(@alignCast(new_ptr)));
+                const node: *BufNode = @ptrCast(@alignCast(new_ptr));
                 node.* = .{ .data = total_size };
                 self.state.buffer_list.first = node;
             }
@@ -167,7 +166,7 @@ pub const ArenaAllocator = struct {
         const log2_align = comptime std.math.log2_int(usize, @alignOf(BufNode));
         const ptr = self.child_allocator.rawAlloc(len, log2_align, @returnAddress()) orelse
             return null;
-        const buf_node = @as(*BufNode, @ptrCast(@alignCast(ptr)));
+        const buf_node: *BufNode = @ptrCast(@alignCast(ptr));
         buf_node.* = .{ .data = len };
         self.state.buffer_list.prepend(buf_node);
         self.state.end_index = 0;
@@ -175,7 +174,7 @@ pub const ArenaAllocator = struct {
     }
 
     fn alloc(ctx: *anyopaque, n: usize, log2_ptr_align: u8, ra: usize) ?[*]u8 {
-        const self = @as(*ArenaAllocator, @ptrCast(@alignCast(ctx)));
+        const self: *ArenaAllocator = @ptrCast(@alignCast(ctx));
         _ = ra;
 
         const ptr_align = @as(usize, 1) << @as(Allocator.Log2Align, @intCast(log2_ptr_align));
@@ -209,7 +208,7 @@ pub const ArenaAllocator = struct {
     }
 
     fn resize(ctx: *anyopaque, buf: []u8, log2_buf_align: u8, new_len: usize, ret_addr: usize) bool {
-        const self = @as(*ArenaAllocator, @ptrCast(@alignCast(ctx)));
+        const self: *ArenaAllocator = @ptrCast(@alignCast(ctx));
         _ = log2_buf_align;
         _ = ret_addr;
 
@@ -236,7 +235,7 @@ pub const ArenaAllocator = struct {
         _ = log2_buf_align;
         _ = ret_addr;
 
-        const self = @as(*ArenaAllocator, @ptrCast(@alignCast(ctx)));
+        const self: *ArenaAllocator = @ptrCast(@alignCast(ctx));
 
         const cur_node = self.state.buffer_list.first orelse return;
         const cur_buf = @as([*]u8, @ptrCast(cur_node))[@sizeOf(BufNode)..cur_node.data];
diff --git a/src/bun.js/bindings/BunString.cpp b/src/bun.js/bindings/BunString.cpp
index 630d9be76684a0..09b545cba08807 100644
--- a/src/bun.js/bindings/BunString.cpp
+++ b/src/bun.js/bindings/BunString.cpp
@@ -96,6 +96,17 @@ BunString fromJS(JSC::JSGlobalObject* globalObject, JSValue value)
     return { BunStringTag::WTFStringImpl, { .wtf = wtfString.impl() } };
 }
 
+extern "C" void BunString__toThreadSafe(BunString* str)
+{
+    if (str->tag == BunStringTag::WTFStringImpl) {
+        auto impl = str->impl.wtf->isolatedCopy();
+        if (impl.ptr() != str->impl.wtf) {
+            impl->ref();
+            str->impl.wtf = &impl.leakRef();
+        }
+    }
+}
+
 BunString toString(JSC::JSGlobalObject* globalObject, JSValue value)
 {
     return fromJS(globalObject, value);
diff --git a/src/bun.js/node/node_fs.zig b/src/bun.js/node/node_fs.zig
index 2068cca3f3a853..826fde635a39d8 100644
--- a/src/bun.js/node/node_fs.zig
+++ b/src/bun.js/node/node_fs.zig
@@ -74,6 +74,7 @@ pub const AsyncReaddirTask = struct {
             .arena = arena,
         };
         task.ref.ref(vm);
+        task.args.path.toThreadSafe();
 
         JSC.WorkPool.schedule(&task.task);
 
@@ -157,6 +158,7 @@ pub const AsyncStatTask = struct {
             .arena = arena,
         };
         task.ref.ref(vm);
+        task.args.path.toThreadSafe();
 
         JSC.WorkPool.schedule(&task.task);
 
@@ -240,6 +242,7 @@ pub const AsyncReadFileTask = struct {
             .arena = arena,
         };
         task.ref.ref(vm);
+        task.args.path.toThreadSafe();
 
         JSC.WorkPool.schedule(&task.task);
 
@@ -904,7 +907,7 @@ pub const Arguments = struct {
         }
 
         pub fn fromJS(ctx: JSC.C.JSContextRef, arguments: *ArgumentsSlice, exception: JSC.C.ExceptionRef) ?Stat {
-            const path = PathLike.fromJS(ctx, arguments, exception) orelse {
+            const path = PathLike.fromJSWithAllocator(ctx, arguments, bun.default_allocator, exception) orelse {
                 if (exception.* == null) {
                     JSC.throwInvalidArguments(
                         "path must be a string or TypedArray",
@@ -1405,7 +1408,7 @@ pub const Arguments = struct {
         }
 
         pub fn fromJS(ctx: JSC.C.JSContextRef, arguments: *ArgumentsSlice, exception: JSC.C.ExceptionRef) ?Readdir {
-            const path = PathLike.fromJS(ctx, arguments, exception) orelse {
+            const path = PathLike.fromJSWithAllocator(ctx, arguments, bun.default_allocator, exception) orelse {
                 if (exception.* == null) {
                     JSC.throwInvalidArguments(
                         "path must be a string or TypedArray",
@@ -1972,7 +1975,7 @@ pub const Arguments = struct {
         }
 
         pub fn fromJS(ctx: JSC.C.JSContextRef, arguments: *ArgumentsSlice, exception: JSC.C.ExceptionRef) ?ReadFile {
-            const path = PathOrFileDescriptor.fromJS(ctx, arguments, arguments.arena.allocator(), exception) orelse {
+            const path = PathOrFileDescriptor.fromJS(ctx, arguments, bun.default_allocator, exception) orelse {
                 if (exception.* == null) {
                     JSC.throwInvalidArguments(
                         "path must be a string or a file descriptor",
diff --git a/src/bun.js/node/types.zig b/src/bun.js/node/types.zig
index 81073463a9c2f5..3ba3db5b94b0c3 100644
--- a/src/bun.js/node/types.zig
+++ b/src/bun.js/node/types.zig
@@ -629,6 +629,12 @@ pub const PathLike = union(Tag) {
         }
     }
 
+    pub fn toThreadSafe(this: *PathLike) void {
+        if (this.* == .slice_with_underlying_string) {
+            this.slice_with_underlying_string.toThreadSafe();
+        }
+    }
+
     pub fn deinitAndUnprotect(this: *const PathLike) void {
         switch (this.*) {
             .slice_with_underlying_string => |val| {
@@ -1050,6 +1056,12 @@ pub const PathOrFileDescriptor = union(Tag) {
         }
     }
 
+    pub fn toThreadSafe(this: *PathOrFileDescriptor) void {
+        if (this.* == .path) {
+            this.path.toThreadSafe();
+        }
+    }
+
     pub fn deinitAndUnprotect(this: PathOrFileDescriptor) void {
         if (this == .path) {
             this.path.deinitAndUnprotect();
diff --git a/src/string.zig b/src/string.zig
index 4fb6e001a0bb1a..9002234cf37caf 100644
--- a/src/string.zig
+++ b/src/string.zig
@@ -829,6 +829,13 @@ pub const String = extern struct {
         return bun.strings.eqlLong(this.byteSlice(), value, true);
     }
 
+    extern fn BunString__toThreadSafe(this: *String) void;
+    pub fn toThreadSafe(this: *String) void {
+        if (this.tag == .WTFStringImpl) {
+            BunString__toThreadSafe(this);
+        }
+    }
+
     pub fn eql(this: String, other: String) bool {
         return this.toZigString().eql(other.toZigString());
     }
@@ -838,6 +845,23 @@ pub const SliceWithUnderlyingString = struct {
     utf8: ZigString.Slice,
     underlying: String,
 
+    pub fn toThreadSafe(this: *SliceWithUnderlyingString) void {
+        std.debug.assert(this.underlying.tag == .WTFStringImpl);
+
+        var orig = this.underlying.value.WTFStringImpl;
+        this.underlying.toThreadSafe();
+        if (this.underlying.value.WTFStringImpl != orig) {
+            orig.deref();
+
+            if (this.utf8.allocator.get()) |allocator| {
+                if (String.isWTFAllocator(allocator)) {
+                    this.utf8.deinit();
+                    this.utf8 = this.underlying.toUTF8(bun.default_allocator);
+                }
+            }
+        }
+    }
+
     pub fn deinit(this: SliceWithUnderlyingString) void {
         this.utf8.deinit();
         this.underlying.deref();
diff --git a/test/js/node/fs/fs.test.ts b/test/js/node/fs/fs.test.ts
index 17c010fb63abb2..86e64b7132740e 100644
--- a/test/js/node/fs/fs.test.ts
+++ b/test/js/node/fs/fs.test.ts
@@ -229,6 +229,39 @@ it("promises.readFile", async () => {
   }
 });
 
+it("promises.readFile - UTF16 file path", async () => {
+  const dest = `/tmp/superduperduperdupduperdupersuperduperduperduperduperduperdupersuperduperduperduperduperduperdupersuperduperduperdupe-Bun-👍-${Date.now()}-${
+    (Math.random() * 1024000) | 0
+  }.txt`;
+  await fs.promises.copyFile(import.meta.path, dest);
+  const expected = readFileSync(import.meta.path, "utf-8");
+  Bun.gc(true);
+  for (let i = 0; i < 100; i++) {
+    expect(await fs.promises.readFile(dest, "utf-8")).toEqual(expected);
+  }
+  Bun.gc(true);
+});
+
+it("promises.readFile - atomized file path", async () => {
+  const destInput = `/tmp/superduperduperdupduperdupersuperduperduperduperduperduperdupersuperduperduperduperduperduperdupersuperduperduperdupe-Bun-👍-${Date.now()}-${
+    (Math.random() * 1024000) | 0
+  }.txt`;
+  // Force it to become an atomized string by making it a property access
+  const dest: string = (
+    {
+      [destInput]: destInput,
+      boop: 123,
+    } as const
+  )[destInput] as string;
+  await fs.promises.copyFile(import.meta.path, dest);
+  const expected = readFileSync(import.meta.path, "utf-8");
+  Bun.gc(true);
+  for (let i = 0; i < 100; i++) {
+    expect(await fs.promises.readFile(dest, "utf-8")).toEqual(expected);
+  }
+  Bun.gc(true);
+});
+
 it("promises.readFile with buffer as file path", async () => {
   for (let i = 0; i < 10; i++)
     expect(await fs.promises.readFile(Buffer.from(import.meta.path), "utf-8")).toEqual(