diff --git a/src/codegen.cpp b/src/codegen.cpp
index d21ada1b23a5..cd38ab3cdabf 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -7849,6 +7849,28 @@ Buf *codegen_generate_builtin_source(CodeGen *g) {
         //assert(EndianBig == 0);
         //assert(EndianLittle == 1);
     }
+    {
+        buf_appendf(contents,
+        "pub const SubSystem = enum {\n"
+        "    Console,\n"
+        "    Windows,\n"
+        "    Posix,\n"
+        "    Native,\n"
+        "    EfiApplication,\n"
+        "    EfiBootServiceDriver,\n"
+        "    EfiRom,\n"
+        "    EfiRuntimeDriver,\n"
+        "};\n\n");
+
+        assert(TargetSubsystemConsole == 1);
+        assert(TargetSubsystemWindows == 2);
+        assert(TargetSubsystemPosix == 3);
+        assert(TargetSubsystemNative == 4);
+        assert(TargetSubsystemEfiApplication == 5);
+        assert(TargetSubsystemEfiBootServiceDriver == 6);
+        assert(TargetSubsystemEfiRom == 7);
+        assert(TargetSubsystemEfiRuntimeDriver == 8);
+    }
     {
         const char *endian_str = g->is_big_endian ? "Endian.Big" : "Endian.Little";
         buf_appendf(contents, "pub const endian = %s;\n", endian_str);
@@ -7865,6 +7887,32 @@ Buf *codegen_generate_builtin_source(CodeGen *g) {
     buf_appendf(contents, "pub const valgrind_support = %s;\n", bool_to_str(want_valgrind_support(g)));
     buf_appendf(contents, "pub const position_independent_code = %s;\n", bool_to_str(g->have_pic));
 
+    {
+        static const char* subsystem_strings[] = {
+            "Console",
+            "Windows",
+            "Posix",
+            "Native",
+            "EfiApplication",
+            "EfiBootServiceDriver",
+            "EfiRom",
+            "EfiRuntimeDriver",
+        };
+
+        if (g->zig_target->os != OsWindows || g->zig_target->os != OsUefi || g->have_dllmain_crt_startup || g->out_type == OutTypeLib) {
+                buf_appendf(contents, "pub const subsystem = null;\n");
+        } else if (g->subsystem == TargetSubsystemAuto) {
+            if (g->have_c_main || g->have_pub_main) {
+                buf_appendf(contents, "pub const subsystem = SubSystem.%s;\n", subsystem_strings[TargetSubsystemConsole - 1]);
+            } else if (g->have_winmain || g->have_winmain_crt_startup) {
+                buf_appendf(contents, "pub const subsystem = SubSystem.%s;\n", subsystem_strings[TargetSubsystemWindows - 1]);
+            }
+        } else {
+            buf_appendf(contents, "pub const subsystem = SubSystem.%s;\n", subsystem_strings[g->subsystem - 1]);
+        }
+        
+    }
+
     if (g->is_test_build) {
         buf_appendf(contents,
             "const TestFn = struct {\n"
@@ -7908,6 +7956,7 @@ static Error define_builtin_compile_vars(CodeGen *g) {
     cache_bool(&cache_hash, g->have_err_ret_tracing);
     cache_bool(&cache_hash, g->libc_link_lib != nullptr);
     cache_bool(&cache_hash, g->valgrind_support);
+    cache_int(&cache_hash, g->subsystem - 1);
 
     Buf digest = BUF_INIT;
     buf_resize(&digest, 0);