diff --git a/src/mingw.zig b/src/mingw.zig
index c10dcbe3f0..8738bcbbcd 100644
--- a/src/mingw.zig
+++ b/src/mingw.zig
@@ -92,6 +92,12 @@ pub fn buildCRTFile(comp: *Compilation, crt_file: CRTFile) !void {
                     "-D_WIN32_WINNT=0x0f00",
                     "-D__MSVCRT_VERSION__=0x700",
                 });
+                if (std.mem.eql(u8, dep, "tlssup.c") and comp.bin_file.options.lto) {
+                    // LLD will incorrectly drop the `_tls_index` symbol. Here we work
+                    // around it by not using LTO for this one file.
+                    // https://github.com/ziglang/zig/issues/8531
+                    try args.append("-fno-lto");
+                }
                 c_source_files[i] = .{
                     .src_path = try comp.zig_lib_directory.join(arena, &[_][]const u8{
                         "libc", "mingw", "crt", dep,
diff --git a/test/standalone.zig b/test/standalone.zig
index f0a783a8a9..35d30fafca 100644
--- a/test/standalone.zig
+++ b/test/standalone.zig
@@ -13,12 +13,27 @@ pub fn addCases(cases: *tests.StandaloneContext) void {
     cases.addBuildFile("test/standalone/main_pkg_path/build.zig", .{});
     cases.addBuildFile("test/standalone/shared_library/build.zig", .{});
     cases.addBuildFile("test/standalone/mix_o_files/build.zig", .{});
+    if (builtin.os.tag == .macos) {
+        // Zig's macOS linker does not yet support LTO for LLVM IR files:
+        // https://github.com/ziglang/zig/issues/8680
+        cases.addBuildFile("test/standalone/mix_c_files/build.zig", .{
+            .build_modes = false,
+            .cross_targets = true,
+        });
+    } else {
+        cases.addBuildFile("test/standalone/mix_c_files/build.zig", .{
+            .build_modes = true,
+            .cross_targets = true,
+        });
+    }
     cases.addBuildFile("test/standalone/global_linkage/build.zig", .{});
     cases.addBuildFile("test/standalone/static_c_lib/build.zig", .{});
     cases.addBuildFile("test/standalone/link_interdependent_static_c_libs/build.zig", .{});
     cases.addBuildFile("test/standalone/link_static_lib_as_system_lib/build.zig", .{});
     cases.addBuildFile("test/standalone/link_common_symbols/build.zig", .{});
-    cases.addBuildFile("test/standalone/link_frameworks/build.zig", .{ .requires_macos_sdk = true });
+    cases.addBuildFile("test/standalone/link_frameworks/build.zig", .{
+        .requires_macos_sdk = true,
+    });
     cases.addBuildFile("test/standalone/issue_339/build.zig", .{});
     cases.addBuildFile("test/standalone/issue_8550/build.zig", .{});
     cases.addBuildFile("test/standalone/issue_794/build.zig", .{});
@@ -33,10 +48,14 @@ pub fn addCases(cases: *tests.StandaloneContext) void {
     if (builtin.os.tag != .wasi) {
         cases.addBuildFile("test/standalone/load_dynamic_library/build.zig", .{});
     }
-    if (builtin.cpu.arch == .x86_64) { // TODO add C ABI support for other architectures
+    // C ABI compatibility issue: https://github.com/ziglang/zig/issues/1481
+    if (builtin.cpu.arch == .x86_64) {
         cases.addBuildFile("test/stage1/c_abi/build.zig", .{});
     }
-    cases.addBuildFile("test/standalone/c_compiler/build.zig", .{ .build_modes = true, .cross_targets = true });
+    cases.addBuildFile("test/standalone/c_compiler/build.zig", .{
+        .build_modes = true,
+        .cross_targets = true,
+    });
 
     if (builtin.os.tag == .windows) {
         cases.addC("test/standalone/issue_9402/main.zig");
@@ -46,7 +65,10 @@ pub fn addCases(cases: *tests.StandaloneContext) void {
         cases.addBuildFile("test/standalone/pie/build.zig", .{});
     }
     // Try to build and run an Objective-C executable.
-    cases.addBuildFile("test/standalone/objc/build.zig", .{ .build_modes = true, .requires_macos_sdk = true });
+    cases.addBuildFile("test/standalone/objc/build.zig", .{
+        .build_modes = true,
+        .requires_macos_sdk = true,
+    });
 
     // Ensure the development tools are buildable.
     cases.add("tools/gen_spirv_spec.zig");
diff --git a/test/standalone/c_compiler/build.zig b/test/standalone/c_compiler/build.zig
index c1efb160ef..aa7217976e 100644
--- a/test/standalone/c_compiler/build.zig
+++ b/test/standalone/c_compiler/build.zig
@@ -3,6 +3,7 @@ const builtin = @import("builtin");
 const Builder = std.build.Builder;
 const CrossTarget = std.zig.CrossTarget;
 
+// TODO integrate this with the std.build executor API
 fn isRunnableTarget(t: CrossTarget) bool {
     if (t.isNative()) return true;
 
@@ -30,12 +31,9 @@ pub fn build(b: *Builder) void {
     exe_cpp.setTarget(target);
     exe_cpp.linkSystemLibrary("c++");
 
-    // disable broken LTO links:
     switch (target.getOsTag()) {
-        .windows => {
-            exe_cpp.want_lto = false;
-        },
         .macos => {
+            // https://github.com/ziglang/zig/issues/8680
             exe_cpp.want_lto = false;
             exe_c.want_lto = false;
         },
diff --git a/test/standalone/mix_c_files/build.zig b/test/standalone/mix_c_files/build.zig
new file mode 100644
index 0000000000..68486ea18d
--- /dev/null
+++ b/test/standalone/mix_c_files/build.zig
@@ -0,0 +1,32 @@
+const std = @import("std");
+const builtin = @import("builtin");
+const Builder = std.build.Builder;
+const CrossTarget = std.zig.CrossTarget;
+
+// TODO integrate this with the std.build executor API
+fn isRunnableTarget(t: CrossTarget) bool {
+    if (t.isNative()) return true;
+
+    return (t.getOsTag() == builtin.os.tag and
+        t.getCpuArch() == builtin.cpu.arch);
+}
+
+pub fn build(b: *Builder) void {
+    const mode = b.standardReleaseOptions();
+    const target = b.standardTargetOptions(.{});
+
+    const exe = b.addExecutable("test", "main.zig");
+    exe.addCSourceFile("test.c", &[_][]const u8{"-std=c11"});
+    exe.setBuildMode(mode);
+    exe.linkLibC();
+    exe.setTarget(target);
+    b.default_step.dependOn(&exe.step);
+
+    const test_step = b.step("test", "Test the program");
+    if (isRunnableTarget(target)) {
+        const run_cmd = exe.run();
+        test_step.dependOn(&run_cmd.step);
+    } else {
+        test_step.dependOn(&exe.step);
+    }
+}
diff --git a/test/standalone/mix_c_files/main.zig b/test/standalone/mix_c_files/main.zig
new file mode 100644
index 0000000000..913d284fe9
--- /dev/null
+++ b/test/standalone/mix_c_files/main.zig
@@ -0,0 +1,30 @@
+const std = @import("std");
+
+extern fn add_C(x: i32) i32;
+extern fn add_C_zig(x: i32) i32;
+extern threadlocal var C_k: c_int;
+
+export var zig_k: c_int = 1;
+export fn add_zig(x: i32) i32 {
+    return x + zig_k + C_k;
+}
+export fn add_may_panic(x: i32) i32 {
+    if (x < 0) @panic("negative int");
+    return x + zig_k;
+}
+
+pub fn main() anyerror!void {
+    var x: i32 = 0;
+    x = add_zig(x);
+    x = add_C(x);
+    x = add_C_zig(x);
+
+    C_k = 200;
+    zig_k = 2;
+    x = add_zig(x);
+    x = add_C(x);
+    x = add_C_zig(x);
+
+    const u = @intCast(u32, x);
+    try std.testing.expect(u / 100 == u % 100);
+}
diff --git a/test/standalone/mix_c_files/test.c b/test/standalone/mix_c_files/test.c
new file mode 100644
index 0000000000..e8ea24ca96
--- /dev/null
+++ b/test/standalone/mix_c_files/test.c
@@ -0,0 +1,8 @@
+
+extern int zig_k;
+extern int add_may_panic(int);
+
+_Thread_local int  C_k = 100;
+int unused(int x) { return x*x; }
+int add_C(int x) { return x+zig_k+C_k; }
+int add_C_zig(int x) { return add_may_panic(x) + C_k; }