diff --git a/CMakeLists.txt b/CMakeLists.txt
index 31d72a34d6..ae8c0e05d1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -591,6 +591,7 @@ set(ZIG_STAGE2_SOURCES
     "${CMAKE_SOURCE_DIR}/src/link/MachO/bind.zig"
     "${CMAKE_SOURCE_DIR}/src/link/MachO/dead_strip.zig"
     "${CMAKE_SOURCE_DIR}/src/link/MachO/fat.zig"
+    "${CMAKE_SOURCE_DIR}/src/link/MachO/hasher.zig"
     "${CMAKE_SOURCE_DIR}/src/link/MachO/load_commands.zig"
     "${CMAKE_SOURCE_DIR}/src/link/MachO/thunks.zig"
     "${CMAKE_SOURCE_DIR}/src/link/MachO/uuid.zig"
diff --git a/src/link/MachO.zig b/src/link/MachO.zig
index f83338f48b..8a8525ab19 100644
--- a/src/link/MachO.zig
+++ b/src/link/MachO.zig
@@ -99,10 +99,10 @@ page_size: u16,
 /// fashion (default for LLVM backend).
 mode: enum { incremental, one_shot },
 
-uuid: macho.uuid_command = .{
-    .cmdsize = @sizeOf(macho.uuid_command),
-    .uuid = undefined,
-},
+uuid: struct {
+    buf: [16]u8 = undefined,
+    final: bool = false,
+} = .{},
 
 dylibs: std.ArrayListUnmanaged(Dylib) = .{},
 dylibs_map: std.StringHashMapUnmanaged(u16) = .{},
@@ -588,11 +588,11 @@ pub fn flushModule(self: *MachO, comp: *Compilation, prog_node: *std.Progress.No
 
     try load_commands.writeBuildVersionLC(&self.base.options, &ncmds, lc_writer);
 
-    {
-        std.crypto.random.bytes(&self.uuid.uuid);
-        try lc_writer.writeStruct(self.uuid);
-        ncmds += 1;
+    if (!self.uuid.final) {
+        std.crypto.random.bytes(&self.uuid.buf);
+        self.uuid.final = true;
     }
+    try load_commands.writeUuidLC(&self.uuid.buf, &ncmds, lc_writer);
 
     try load_commands.writeLoadDylibLCs(self.dylibs.items, self.referenced_dylibs.keys(), &ncmds, lc_writer);
 
diff --git a/src/link/MachO/CodeSignature.zig b/src/link/MachO/CodeSignature.zig
index e3c362e941..391ac28efa 100644
--- a/src/link/MachO/CodeSignature.zig
+++ b/src/link/MachO/CodeSignature.zig
@@ -1,6 +1,4 @@
 const CodeSignature = @This();
-const Compilation = @import("../../Compilation.zig");
-const WaitGroup = @import("../../WaitGroup.zig");
 
 const std = @import("std");
 const assert = std.debug.assert;
@@ -9,10 +7,13 @@ const log = std.log.scoped(.link);
 const macho = std.macho;
 const mem = std.mem;
 const testing = std.testing;
+
 const Allocator = mem.Allocator;
+const Compilation = @import("../../Compilation.zig");
+const Hasher = @import("hasher.zig").ParallelHasher;
 const Sha256 = std.crypto.hash.sha2.Sha256;
 
-const hash_size: u8 = 32;
+const hash_size = Sha256.digest_length;
 
 const Blob = union(enum) {
     code_directory: *CodeDirectory,
@@ -109,7 +110,7 @@ const CodeDirectory = struct {
     fn size(self: CodeDirectory) u32 {
         const code_slots = self.inner.nCodeSlots * hash_size;
         const special_slots = self.inner.nSpecialSlots * hash_size;
-        return @sizeOf(macho.CodeDirectory) + @intCast(u32, self.ident.len + 1) + special_slots + code_slots;
+        return @sizeOf(macho.CodeDirectory) + @intCast(u32, self.ident.len + 1 + special_slots + code_slots);
     }
 
     fn write(self: CodeDirectory, writer: anytype) !void {
@@ -287,33 +288,11 @@ pub fn writeAdhocSignature(
     self.code_directory.inner.nCodeSlots = total_pages;
 
     // Calculate hash for each page (in file) and write it to the buffer
-    var wg: WaitGroup = .{};
-    {
-        const buffer = try gpa.alloc(u8, self.page_size * total_pages);
-        defer gpa.free(buffer);
-
-        const results = try gpa.alloc(fs.File.PReadError!usize, total_pages);
-        defer gpa.free(results);
-        {
-            wg.reset();
-            defer wg.wait();
-
-            var i: usize = 0;
-            while (i < total_pages) : (i += 1) {
-                const fstart = i * self.page_size;
-                const fsize = if (fstart + self.page_size > opts.file_size)
-                    opts.file_size - fstart
-                else
-                    self.page_size;
-                const out_hash = &self.code_directory.code_slots.items[i];
-                wg.start();
-                try comp.thread_pool.spawn(workerSha256Hash, .{
-                    opts.file, fstart, buffer[fstart..][0..fsize], out_hash, &results[i], &wg,
-                });
-            }
-        }
-        for (results) |result| _ = try result;
-    }
+    var hasher = Hasher(Sha256){};
+    try hasher.hash(gpa, comp.thread_pool, opts.file, self.code_directory.code_slots.items, .{
+        .chunk_size = self.page_size,
+        .max_file_size = opts.file_size,
+    });
 
     try blobs.append(.{ .code_directory = &self.code_directory });
     header.length += @sizeOf(macho.BlobIndex);
@@ -352,7 +331,7 @@ pub fn writeAdhocSignature(
     }
 
     self.code_directory.inner.hashOffset =
-        @sizeOf(macho.CodeDirectory) + @intCast(u32, self.code_directory.ident.len + 1) + self.code_directory.inner.nSpecialSlots * hash_size;
+        @sizeOf(macho.CodeDirectory) + @intCast(u32, self.code_directory.ident.len + 1 + self.code_directory.inner.nSpecialSlots * hash_size);
     self.code_directory.inner.length = self.code_directory.size();
     header.length += self.code_directory.size();
 
@@ -372,19 +351,6 @@ pub fn writeAdhocSignature(
     }
 }
 
-fn workerSha256Hash(
-    file: fs.File,
-    fstart: usize,
-    buffer: []u8,
-    hash: *[hash_size]u8,
-    err: *fs.File.PReadError!usize,
-    wg: *WaitGroup,
-) void {
-    defer wg.finish();
-    err.* = file.preadAll(buffer, fstart);
-    Sha256.hash(buffer, hash, .{});
-}
-
 pub fn size(self: CodeSignature) u32 {
     var ssize: u32 = @sizeOf(macho.SuperBlob) + @sizeOf(macho.BlobIndex) + self.code_directory.size();
     if (self.requirements) |req| {
diff --git a/src/link/MachO/DebugSymbols.zig b/src/link/MachO/DebugSymbols.zig
index 655ba7162f..22905a520a 100644
--- a/src/link/MachO/DebugSymbols.zig
+++ b/src/link/MachO/DebugSymbols.zig
@@ -5,6 +5,7 @@ const build_options = @import("build_options");
 const assert = std.debug.assert;
 const fs = std.fs;
 const link = @import("../../link.zig");
+const load_commands = @import("load_commands.zig");
 const log = std.log.scoped(.dsym);
 const macho = std.macho;
 const makeStaticString = MachO.makeStaticString;
@@ -303,10 +304,7 @@ pub fn flushModule(self: *DebugSymbols, macho_file: *MachO) !void {
     self.finalizeDwarfSegment(macho_file);
     try self.writeLinkeditSegmentData(macho_file, &ncmds, lc_writer);
 
-    {
-        try lc_writer.writeStruct(macho_file.uuid);
-        ncmds += 1;
-    }
+    try load_commands.writeUuidLC(&macho_file.uuid.buf, &ncmds, lc_writer);
 
     var headers_buf = std.ArrayList(u8).init(self.allocator);
     defer headers_buf.deinit();
diff --git a/src/link/MachO/hasher.zig b/src/link/MachO/hasher.zig
new file mode 100644
index 0000000000..29099ad2d9
--- /dev/null
+++ b/src/link/MachO/hasher.zig
@@ -0,0 +1,60 @@
+const std = @import("std");
+const assert = std.debug.assert;
+const fs = std.fs;
+const mem = std.mem;
+
+const Allocator = mem.Allocator;
+const ThreadPool = @import("../../ThreadPool.zig");
+const WaitGroup = @import("../../WaitGroup.zig");
+
+pub fn ParallelHasher(comptime Hasher: type) type {
+    const hash_size = Hasher.digest_length;
+
+    return struct {
+        pub fn hash(self: @This(), gpa: Allocator, pool: *ThreadPool, file: fs.File, out: [][hash_size]u8, opts: struct {
+            chunk_size: u16 = 0x4000,
+            max_file_size: ?u64 = null,
+        }) !void {
+            _ = self;
+
+            var wg: WaitGroup = .{};
+
+            const file_size = opts.max_file_size orelse try file.getEndPos();
+            const total_num_chunks = mem.alignForward(file_size, opts.chunk_size) / opts.chunk_size;
+            assert(out.len >= total_num_chunks);
+
+            const buffer = try gpa.alloc(u8, opts.chunk_size * total_num_chunks);
+            defer gpa.free(buffer);
+
+            const results = try gpa.alloc(fs.File.PReadError!usize, total_num_chunks);
+            defer gpa.free(results);
+
+            {
+                wg.reset();
+                defer wg.wait();
+
+                var i: usize = 0;
+                while (i < total_num_chunks) : (i += 1) {
+                    const fstart = i * opts.chunk_size;
+                    const fsize = if (fstart + opts.chunk_size > file_size) file_size - fstart else opts.chunk_size;
+                    wg.start();
+                    try pool.spawn(worker, .{ file, fstart, buffer[fstart..][0..fsize], &out[i], &results[i], &wg });
+                }
+            }
+            for (results) |result| _ = try result;
+        }
+
+        fn worker(
+            file: fs.File,
+            fstart: usize,
+            buffer: []u8,
+            out: *[hash_size]u8,
+            err: *fs.File.PReadError!usize,
+            wg: *WaitGroup,
+        ) void {
+            defer wg.finish();
+            err.* = file.preadAll(buffer, fstart);
+            Hasher.hash(buffer, out, .{});
+        }
+    };
+}
diff --git a/src/link/MachO/uuid.zig b/src/link/MachO/uuid.zig
new file mode 100644
index 0000000000..987b156a4b
--- /dev/null
+++ b/src/link/MachO/uuid.zig
@@ -0,0 +1,69 @@
+const std = @import("std");
+const fs = std.fs;
+const mem = std.mem;
+
+const Allocator = mem.Allocator;
+const Compilation = @import("../../Compilation.zig");
+const Md5 = std.crypto.hash.Md5;
+const Hasher = @import("hasher.zig").ParallelHasher;
+
+/// Somewhat random chunk size for MD5 hash calculation.
+pub const chunk_size = 0x4000;
+
+/// Calculates Md5 hash of the file contents.
+/// Hash is calculated in a streaming manner which may be slow.
+pub fn calcUuidStreaming(file: fs.File, file_size: u64, out: *[Md5.digest_length]u8) !void {
+    const total_num_chunks = mem.alignForward(file_size, chunk_size) / chunk_size;
+
+    var hasher = Md5.init(.{});
+    var buffer: [chunk_size]u8 = undefined;
+
+    var i: usize = 0;
+    while (i < total_num_chunks) : (i += 1) {
+        const start = i * chunk_size;
+        const size = if (start + chunk_size > file_size)
+            file_size - start
+        else
+            chunk_size;
+        const amt = try file.preadAll(&buffer, start);
+        if (amt != size) return error.InputOutput;
+
+        hasher.update(buffer[0..size]);
+    }
+
+    hasher.final(out);
+    conform(out);
+}
+
+/// Calculates Md5 hash of each chunk in parallel and then hashes all Md5 hashes to produce
+/// the final digest.
+/// While this is NOT a correct MD5 hash of the contents, this methodology is used by LLVM/LLD
+/// and we will use it too as it seems accepted by Apple OSes.
+pub fn calcUuidParallel(comp: *const Compilation, file: fs.File, file_size: u64, out: *[Md5.digest_length]u8) !void {
+    const total_hashes = mem.alignForward(file_size, chunk_size) / chunk_size;
+
+    const hashes = try comp.gpa.alloc([Md5.digest_length]u8, total_hashes);
+    defer comp.gpa.free(hashes);
+
+    var hasher = Hasher(Md5){};
+    try hasher.hash(comp.gpa, comp.thread_pool, file, hashes, .{
+        .chunk_size = chunk_size,
+        .max_file_size = file_size,
+    });
+
+    const final_buffer = try comp.gpa.alloc(u8, total_hashes * Md5.digest_length);
+    defer comp.gpa.free(final_buffer);
+
+    for (hashes) |hash, i| {
+        mem.copy(u8, final_buffer[i * Md5.digest_length ..][0..Md5.digest_length], &hash);
+    }
+
+    Md5.hash(final_buffer, out, .{});
+    conform(out);
+}
+
+inline fn conform(out: *[Md5.digest_length]u8) void {
+    // LC_UUID uuids should conform to RFC 4122 UUID version 4 & UUID version 5 formats
+    out[6] = (out[6] & 0x0F) | (3 << 4);
+    out[8] = (out[8] & 0x3F) | 0x80;
+}
diff --git a/src/link/MachO/zld.zig b/src/link/MachO/zld.zig
index 9a66d76e1a..022167e223 100644
--- a/src/link/MachO/zld.zig
+++ b/src/link/MachO/zld.zig
@@ -4037,8 +4037,15 @@ pub fn linkWithZld(macho_file: *MachO, comp: *Compilation, prog_node: *std.Progr
         const uuid_offset_backpatch: ?usize = blk: {
             const index = lc_buffer.items.len;
             var uuid_buf: [16]u8 = [_]u8{0} ** 16;
+
+            if (zld.options.optimize_mode == .Debug) {
+                // In Debug we don't really care about reproducibility, so put in a random value
+                // and be done with it.
+                std.crypto.random.bytes(&uuid_buf);
+            }
+
             try load_commands.writeUuidLC(&uuid_buf, &ncmds, lc_writer);
-            break :blk index;
+            break :blk if (zld.options.optimize_mode == .Debug) null else index;
         };
 
         try load_commands.writeLoadDylibLCs(zld.dylibs.items, zld.referenced_dylibs.keys(), &ncmds, lc_writer);
@@ -4076,7 +4083,7 @@ pub fn linkWithZld(macho_file: *MachO, comp: *Compilation, prog_node: *std.Progr
             const seg = zld.getLinkeditSegmentPtr();
             const file_size = seg.fileoff + seg.filesize;
             var uuid_buf: [16]u8 = undefined;
-            try uuid.calcMd5Hash(zld.gpa, zld.file, file_size, &uuid_buf);
+            try uuid.calcUuidParallel(comp, zld.file, file_size, &uuid_buf);
             const offset = @sizeOf(macho.mach_header_64) + headers_buf.items.len + backpatch + @sizeOf(macho.load_command);
             try zld.file.pwriteAll(&uuid_buf, offset);
         }