diff --git a/packages/natives/scripts/build-native.ts b/packages/natives/scripts/build-native.ts
index 2778b87fe..194f9faea 100644
--- a/packages/natives/scripts/build-native.ts
+++ b/packages/natives/scripts/build-native.ts
@@ -376,11 +376,15 @@ if (crossTarget) {
 	// enforces per-function target features: opus' silk/x86 SSE4.1 units fail to
 	// build without the feature enabled globally. The win32 x64 addon floor is
 	// x86-64-v2 (SSE4.2 inclusive), so enabling it for all C deps is safe.
+	// cargo-xwin overwrites `CFLAGS_<target>` on the cargo it spawns but appends
+	// the plain `CFLAGS`/`CXXFLAGS` values into it, so those are the only knobs
+	// that survive.
 	if (crossTarget.endsWith("-msvc") && targetArch === "x64") {
-		const envKey = `CFLAGS_${bareTriple.replace(/-/g, "_")}`;
-		const existing = process.env[envKey] ?? "";
-		const sseFlags = "-msse4.1 -msse4.2";
-		process.env[envKey] = existing ? `${existing} ${sseFlags}` : sseFlags;
+		for (const envKey of ["CFLAGS", "CXXFLAGS"]) {
+			const existing = process.env[envKey] ?? "";
+			const sseFlags = "-msse4.1 -msse4.2";
+			process.env[envKey] = existing ? `${existing} ${sseFlags}` : sseFlags;
+		}
 	}
 	// napi 3.7.0 resolves the built artifact from the FULL `--target` directory,
 	// but cargo-zigbuild writes under the bare triple; bridge the two so napi's