diff --git a/src/Compilation.zig b/src/Compilation.zig
index 9b187614a76bfc115f244004fb055f9d38eb321a..2b2e4ac022a8f705103619b3879609eb3fb84412 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -6342,6 +6342,8 @@ fn addCommonCCArgs(
                 // LLVM doesn't distinguish between Solaris and illumos, but the illumos GCC fork
                 // defines this macro.
                 .illumos => try argv.append("__illumos__"),
+                // This macro has not yet been upstreamed by SerenityOS to Clang.
+                .serenity => try argv.append("__serenity__"),
                 // Homebrew targets without LLVM support; use communities's preferred macros.
                 .@"3ds" => try argv.append("-D__3DS__"),
                 .psp => try argv.append("-D__PSP__"),