diff --git a/src/misc.c b/src/misc.c
index 191e707..6712355 100644
--- a/src/misc.c
+++ b/src/misc.c
@@ -14,6 +14,15 @@
 
 #define PORT_MATH_CLEAR        0x00f0
 
+// Indicator if POST phase has been started (and if it has completed).
+int HaveRunPost VARFSEG;
+
+int
+in_post(void)
+{
+    return GET_GLOBAL(HaveRunPost) == 1;
+}
+
 
 /****************************************************************
  * Misc 16bit ISRs
diff --git a/src/post.c b/src/post.c
index 5fc1968..0d9e66f 100644
--- a/src/post.c
+++ b/src/post.c
@@ -185,6 +185,8 @@
     malloc_prepboot();
     memmap_prepboot();
 
+    HaveRunPost = 2;
+
     // Setup bios checksum.
     BiosChecksum -= checksum((u8*)BUILD_BIOS_ADDR, BUILD_BIOS_SIZE);
 }
diff --git a/src/resume.c b/src/resume.c
index e2ceef1..1903174 100644
--- a/src/resume.c
+++ b/src/resume.c
@@ -17,9 +17,6 @@
 #include "string.h" // memset
 #include "util.h" // dma_setup
 
-// Indicator if POST phase has been run.
-int HaveRunPost VARFSEG;
-
 // Handler for post calls that look like a resume.
 void VISIBLE16
 handle_resume(void)
diff --git a/src/system.c b/src/system.c
index 5d10cc8..3cb2228 100644
--- a/src/system.c
+++ b/src/system.c
@@ -115,12 +115,13 @@
     SET_FARVAR(gdt_seg, gdt_far[1], GDT_DATA | GDT_LIMIT((6*sizeof(u64))-1)
                | GDT_BASE(loc));
     // Initialize CS descriptor
-    SET_FARVAR(gdt_seg, gdt_far[4], GDT_CODE | GDT_LIMIT(BUILD_BIOS_SIZE-1)
-               | GDT_BASE(BUILD_BIOS_ADDR));
+    u64 lim = GDT_LIMIT(0x0ffff);
+    if (in_post())
+        lim = GDT_GRANLIMIT(0xffffffff);
+    SET_FARVAR(gdt_seg, gdt_far[4], GDT_CODE | lim | GDT_BASE(BUILD_BIOS_ADDR));
     // Initialize SS descriptor
     loc = (u32)MAKE_FLATPTR(GET_SEG(SS), 0);
-    SET_FARVAR(gdt_seg, gdt_far[5], GDT_DATA | GDT_LIMIT(0x0ffff)
-               | GDT_BASE(loc));
+    SET_FARVAR(gdt_seg, gdt_far[5], GDT_DATA | lim | GDT_BASE(loc));
 
     u16 count = regs->cx;
     asm volatile(
diff --git a/src/util.h b/src/util.h
index 9557581..0cbea48 100644
--- a/src/util.h
+++ b/src/util.h
@@ -178,6 +178,7 @@
 // misc.c
 extern struct bios_config_table_s BIOS_CONFIG_TABLE __aligned(1);
 extern u8 BiosChecksum;
+int in_post(void);
 void mathcp_setup(void);
 
 // mouse.c