diff --git a/lib/libcrypto/crypto_assembly.h b/lib/libcrypto/crypto_assembly.h
new file mode 100644
index 00000000000..0ae78a81ab3
--- /dev/null
+++ b/lib/libcrypto/crypto_assembly.h
@@ -0,0 +1,30 @@
+/*	$OpenBSD: crypto_assembly.h,v 1.1 2026/03/28 13:09:55 jsing Exp $ */
+/*
+ * Copyright (c) 2026 Joel Sing <jsing@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifndef HEADER_CRYPTO_ASSEMBLY_H
+#define HEADER_CRYPTO_ASSEMBLY_H
+
+/* Ensure _CET_ENDBR is always defined on amd64. */
+#ifdef __amd64__
+#ifdef __CET__
+#include <cet.h>
+#else
+#define _CET_ENDBR
+#endif
+#endif
+
+#endif