diff --git a/src/all_types.hpp b/src/all_types.hpp
index 39bccddc3..5a5c1cfda 100644
--- a/src/all_types.hpp
+++ b/src/all_types.hpp
@@ -1856,6 +1856,7 @@ struct CodeGen {
     bool strip_debug_symbols;
     bool is_test_build;
     bool is_single_threaded;
+    bool want_single_threaded;
     bool linker_rdynamic;
     bool each_lib_rpath;
     bool is_dummy_so;
diff --git a/src/codegen.cpp b/src/codegen.cpp
index 7d280b7ad..332eab59b 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -7337,9 +7337,26 @@ static bool detect_pic(CodeGen *g) {
     zig_unreachable();
 }
 
+static bool detect_single_threaded(CodeGen *g) {
+    if (g->want_single_threaded)
+        return true;
+    if (target_is_single_threaded(g->zig_target)) {
+        return true;
+    }
+    return false;
+}
+
+static bool detect_err_ret_tracing(CodeGen *g) {
+    return !target_is_wasm(g->zig_target) &&
+        g->build_mode != BuildModeFastRelease &&
+        g->build_mode != BuildModeSmallRelease;
+}
+
 Buf *codegen_generate_builtin_source(CodeGen *g) {
     g->have_dynamic_link = detect_dynamic_link(g);
     g->have_pic = detect_pic(g);
+    g->is_single_threaded = detect_single_threaded(g);
+    g->have_err_ret_tracing = detect_err_ret_tracing(g);
 
     Buf *contents = buf_alloc();
 
@@ -7844,6 +7861,12 @@ static void init(CodeGen *g) {
 
     g->have_dynamic_link = detect_dynamic_link(g);
     g->have_pic = detect_pic(g);
+    g->is_single_threaded = detect_single_threaded(g);
+    g->have_err_ret_tracing = detect_err_ret_tracing(g);
+
+    if (target_is_single_threaded(g->zig_target)) {
+        g->is_single_threaded = true;
+    }
 
     if (g->is_test_build) {
         g->subsystem = TargetSubsystemConsole;
@@ -7953,8 +7976,6 @@ static void init(CodeGen *g) {
         }
     }
 
-    g->have_err_ret_tracing = !target_is_wasm(g->zig_target) && g->build_mode != BuildModeFastRelease && g->build_mode != BuildModeSmallRelease;
-
     define_builtin_fns(g);
     Error err;
     if ((err = define_builtin_compile_vars(g))) {
@@ -9268,6 +9289,8 @@ void codegen_build_and_link(CodeGen *g) {
 
     g->have_dynamic_link = detect_dynamic_link(g);
     g->have_pic = detect_pic(g);
+    g->is_single_threaded = detect_single_threaded(g);
+    g->have_err_ret_tracing = detect_err_ret_tracing(g);
     detect_libc(g);
     detect_dynamic_linker(g);
 
diff --git a/src/main.cpp b/src/main.cpp
index e571e1ae6..5123512d1 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -450,7 +450,7 @@ int main(int argc, char **argv) {
     int runtime_args_start = -1;
     bool system_linker_hack = false;
     TargetSubsystem subsystem = TargetSubsystemAuto;
-    bool is_single_threaded = false;
+    bool want_single_threaded = false;
     bool disable_gen_h = false;
     Buf *override_std_dir = nullptr;
     Buf *main_pkg_path = nullptr;
@@ -590,7 +590,7 @@ int main(int argc, char **argv) {
         CodeGen *g = codegen_create(main_pkg_path, fmt_runner_path, &target, OutTypeExe,
                 BuildModeDebug, get_zig_lib_dir(), nullptr, nullptr, cache_dir_buf);
         g->valgrind_support = valgrind_support;
-        g->is_single_threaded = true;
+        g->want_single_threaded = true;
         codegen_set_out_name(g, buf_create_from_str("fmt"));
         g->enable_cache = true;
 
@@ -671,7 +671,7 @@ int main(int argc, char **argv) {
             } else if (strcmp(arg, "--system-linker-hack") == 0) {
                 system_linker_hack = true;
             } else if (strcmp(arg, "--single-threaded") == 0) {
-                is_single_threaded = true;
+                want_single_threaded = true;
             } else if (strcmp(arg, "--disable-gen-h") == 0) {
                 disable_gen_h = true;
             } else if (strcmp(arg, "--test-cmd-bin") == 0) {
@@ -921,10 +921,6 @@ int main(int argc, char **argv) {
         }
     }
 
-    if (target_is_single_threaded(&target)) {
-        is_single_threaded = true;
-    }
-
     if (output_dir != nullptr && enable_cache == CacheOptOn) {
         fprintf(stderr, "`--output-dir` is incompatible with --cache on.\n");
         return print_error_usage(arg0);
@@ -966,7 +962,7 @@ int main(int argc, char **argv) {
                 out_type, build_mode, get_zig_lib_dir(), override_std_dir, nullptr, nullptr);
         g->valgrind_support = valgrind_support;
         g->want_pic = want_pic;
-        g->is_single_threaded = is_single_threaded;
+        g->want_single_threaded = want_single_threaded;
         Buf *builtin_source = codegen_generate_builtin_source(g);
         if (fwrite(buf_ptr(builtin_source), 1, buf_len(builtin_source), stdout) != buf_len(builtin_source)) {
             fprintf(stderr, "unable to write to stdout: %s\n", strerror(ferror(stdout)));
@@ -1064,7 +1060,7 @@ int main(int argc, char **argv) {
             codegen_set_out_name(g, buf_out_name);
             codegen_set_lib_version(g, ver_major, ver_minor, ver_patch);
             codegen_set_is_test(g, cmd == CmdTest);
-            g->is_single_threaded = is_single_threaded;
+            g->want_single_threaded = want_single_threaded;
             codegen_set_linker_script(g, linker_script);
             if (each_lib_rpath)
                 codegen_set_each_lib_rpath(g, each_lib_rpath);