diff --git a/am/include/x86.h b/am/include/x86.h
index 73de4a0f..49a66f34 100644
--- a/am/include/x86.h
+++ b/am/include/x86.h
@@ -1,6 +1,3 @@
-#ifndef __X86_H__
-#define __X86_H__
-
 // CPU rings
 #define DPL_KERN       0x0     // Kernel (ring 0)
 #define DPL_USER       0x3     // User (ring 3)
@@ -120,30 +117,36 @@ typedef struct {
   uint32_t base_31_24 : 8; // High bits of segment base address
 } SegDesc;
 
+#define SEG16(type, base, lim, dpl) (SegDesc)           \
+{ (lim) & 0xffff, (uintptr_t)(base) & 0xffff,            \
+  ((uintptr_t)(base) >> 16) & 0xff, type, 0, dpl, 1,     \
+  (uintptr_t)(lim) >> 16, 0, 0, 1, 0, (uintptr_t)(base) >> 24 }
+
+#define SEG32(type, base, lim, dpl) (SegDesc)           \
+{ ((lim) >> 12) & 0xffff, (uintptr_t)(base) & 0xffff,    \
+  ((uintptr_t)(base) >> 16) & 0xff, type, 1, dpl, 1,     \
+  (uintptr_t)(lim) >> 28, 0, 0, 1, 1, (uintptr_t)(base) >> 24 }
+
 #define SEG64(type, dpl) (SegDesc) \
   { 0, 0, 0, type, 1, dpl, 1, 0, 0, 1, 0, 0 }
 
-#define SEG32(type, base, lim, dpl) (SegDesc)             \
-{  ((lim) >> 12) & 0xffff, (uint32_t)(base) & 0xffff,   \
-  ((uint32_t)(base) >> 16) & 0xff, type, 1, dpl, 1,     \
-  (uint32_t)(lim) >> 28, 0, 0, 1, 1, (uint32_t)(base) >> 24 }
-
-#define SEG16(type, base, lim, dpl) (SegDesc)           \
-{  (lim) & 0xffff, (uint32_t)(base) & 0xffff,           \
+#define SEGTSS64(type, base, lim, dpl) (SegDesc) \
+{ (lim) & 0xffff, (uint32_t)(base) & 0xffff,            \
   ((uint32_t)(base) >> 16) & 0xff, type, 0, dpl, 1,     \
-  (uint32_t)(lim) >> 16, 0, 0, 1, 0, (uint32_t)(base) >> 24 }
+  (uint32_t)(lim) >> 16, 0, 0, 0, 0, (uint32_t)(base) >> 24 }
+
 
 // Gate descriptors for interrupts and traps
 typedef struct {
-  uint32_t off_15_0 : 16;   // Low 16 bits of offset in segment
-  uint32_t cs : 16;         // Code segment selector
-  uint32_t args : 5;        // # args, 0 for interrupt/trap gates
-  uint32_t rsv1 : 3;        // Reserved(should be zero I guess)
-  uint32_t type : 4;        // Type(STS_{TG,IG32,TG32})
-  uint32_t s : 1;           // Must be 0 (system)
-  uint32_t dpl : 2;         // Descriptor(meaning new) privilege level
-  uint32_t p : 1;           // Present
-  uint32_t off_31_16 : 16;  // High bits of offset in segment
+  uint32_t off_15_0  : 16; // Low 16 bits of offset in segment
+  uint32_t cs        : 16; // Code segment selector
+  uint32_t args      :  5; // # args, 0 for interrupt/trap gates
+  uint32_t rsv1      :  3; // Reserved(should be zero I guess)
+  uint32_t type      :  4; // Type(STS_{TG,IG32,TG32})
+  uint32_t s         :  1; // Must be 0 (system)
+  uint32_t dpl       :  2; // Descriptor(meaning new) privilege level
+  uint32_t p         :  1; // Present
+  uint32_t off_31_16 : 16; // High bits of offset in segment
 } GateDesc32;
 
 #define GATE32(type, cs, entry, dpl) (GateDesc32)                \
@@ -151,17 +154,17 @@ typedef struct {
   1, (uint32_t)(entry) >> 16 }
 
 typedef struct {
-  uint32_t off_15_0 : 16;
-  uint32_t cs : 16;
-  uint32_t isv : 3;
-  uint32_t zero1 : 5;
-  uint32_t type : 4;
-  uint32_t zero2 : 1;
-  uint32_t dpl : 2;
-  uint32_t p : 1;
+  uint32_t off_15_0  : 16;
+  uint32_t cs        : 16;
+  uint32_t isv       :  3;
+  uint32_t zero1     :  5;
+  uint32_t type      :  4;
+  uint32_t zero2     :  1;
+  uint32_t dpl       :  2;
+  uint32_t p         :  1;
   uint32_t off_31_16 : 16;
   uint32_t off_63_32 : 32;
-  uint32_t rsv : 32;
+  uint32_t rsv       : 32;
 } GateDesc64;
 
 #define GATE64(type, cs, entry, dpl) (GateDesc64) \
@@ -323,6 +326,4 @@ static inline void stack_switch_call(void *sp, void *entry, uintptr_t arg) {
   );
 }
 
-#endif
-
-#endif
+#endif // __ASSEMBLER__
diff --git a/am/src/x86_64/qemu/trm.c b/am/src/x86_64/qemu/trm.c
index 64b593a0..be6c6836 100644
--- a/am/src/x86_64/qemu/trm.c
+++ b/am/src/x86_64/qemu/trm.c
@@ -97,14 +97,13 @@ void __am_lapic_init() {
 void __am_percpu_initgdt() {
 #if __x86_64__
   SegDesc *gdt = CPU->gdt;
-  uint64_t tss = (uint64_t)(&CPU->tss);
-  gdt[SEG_KCODE] = SEG64(STA_X | STA_R, DPL_KERN);
-  gdt[SEG_KDATA] = SEG64(STA_W,         DPL_KERN);
-  gdt[SEG_UCODE] = SEG64(STA_X | STA_R, DPL_USER);
-  gdt[SEG_UDATA] = SEG64(STA_W,         DPL_USER);
-  ((uint64_t *)gdt)[SEG_TSS+0] = (sizeof(CPU->tss) - 1) | ((tss & 0xffffff) << 16) |
-                   (0x00e9LL << 40) | (((tss >> 24) & 0xff) << 56);
-  ((uint64_t *)gdt)[SEG_TSS+1] = (tss >> 32);
+  TSS64 *tss = &CPU->tss;
+  gdt[SEG_KCODE] = SEG64(STA_X | STA_R,                      DPL_KERN);
+  gdt[SEG_KDATA] = SEG64(STA_W,                              DPL_KERN);
+  gdt[SEG_UCODE] = SEG64(STA_X | STA_R,                      DPL_USER);
+  gdt[SEG_UDATA] = SEG64(STA_W,                              DPL_USER);
+  gdt[SEG_TSS]   = SEG16(STS_T32A,      tss, sizeof(*tss)-1, DPL_KERN);
+  bug_on((uintptr_t)tss >> 32);
   set_gdt(gdt, sizeof(gdt[0]) * (NR_SEG + 1));
   set_tr(KSEL(SEG_TSS));
 #else
diff --git a/am/src/x86_64/qemu/x86_64-qemu.h b/am/src/x86_64/qemu/x86_64-qemu.h
index e4e16bbd..8688b63b 100644
--- a/am/src/x86_64/qemu/x86_64-qemu.h
+++ b/am/src/x86_64/qemu/x86_64-qemu.h
@@ -1,6 +1,3 @@
-#ifndef __X86_64_QEMU_H__
-#define __X86_64_QEMU_H__
-
 #define MAX_CPU               8
 #define BOOT_REC_ADDR   0x07000
 #define ARG_ADDR        0x10000
@@ -132,5 +129,3 @@ void __am_percpu_initlapic();
 void __am_stop_the_world();
 
 #endif
-
-#endif