diff --git a/src/arch/x86/thread.c b/src/arch/x86/thread.c
index a9fda66245..fa6096161b 100644
--- a/src/arch/x86/thread.c
+++ b/src/arch/x86/thread.c
@@ -2,6 +2,10 @@
 
 #include <thread.h>
 
+#if ENV_X86_64
+#error COOP_MULTITASKING does not currently support x86_64
+#endif
+
 /* The stack frame looks like the following after a pushad instruction. */
 struct pushad_regs {
 	uint32_t edi; /* Offset 0x00 */
diff --git a/src/arch/x86/thread_switch.S b/src/arch/x86/thread_switch.S
index 049f092741..3c6a34dd13 100644
--- a/src/arch/x86/thread_switch.S
+++ b/src/arch/x86/thread_switch.S
@@ -1,5 +1,9 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+#if ENV_X86_64
+#error COOP_MULTITASKING does not currently support x86_64
+#endif
+
 .code32
 .text