diff --git a/include/asm-um/ldt-x86_64.h b/include/asm-um/ldt-x86_64.h
index 57159f12dde2..96b35aada79a 100644
--- a/include/asm-um/ldt-x86_64.h
+++ b/include/asm-um/ldt-x86_64.h
@@ -39,11 +39,13 @@ typedef struct uml_ldt {
 } uml_ldt_t;
 
 /*
- * macros stolen from include/asm-i386/desc.h
+ * macros stolen from include/asm-x86_64/desc.h
  */
 #define LDT_entry_a(info) \
 	((((info)->base_addr & 0x0000ffff) << 16) | ((info)->limit & 0x0ffff))
 
+/* Don't allow setting of the lm bit. It is useless anyways because
+ * 64bit system calls require __USER_CS. */
 #define LDT_entry_b(info) \
 	(((info)->base_addr & 0xff000000) | \
 	(((info)->base_addr & 0x00ff0000) >> 16) | \
@@ -54,6 +56,7 @@ typedef struct uml_ldt {
 	((info)->seg_32bit << 22) | \
 	((info)->limit_in_pages << 23) | \
 	((info)->useable << 20) | \
+	/* ((info)->lm << 21) | */ \
 	0x7000)
 
 #define LDT_empty(info) (\
@@ -64,6 +67,7 @@ typedef struct uml_ldt {
 	(info)->seg_32bit	== 0	&& \
 	(info)->limit_in_pages	== 0	&& \
 	(info)->seg_not_present	== 1	&& \
-	(info)->useable		== 0	)
+	(info)->useable		== 0	&& \
+	(info)->lm              == 0)
 
 #endif