diff --git a/arch/x86_64/pmap.c b/arch/x86_64/pmap.c
index 5ba7fbd..9b50eb5 100644
--- a/arch/x86_64/pmap.c
+++ b/arch/x86_64/pmap.c
@@ -19,7 +19,7 @@
 #define PTR_TO_ENTRY(x) (((x) & ~VM_PAGE_MASK) | PTE_PRESENT | PTE_RW | PTE_USR)
 #define ENTRY_TO_PTR(x) ((x) & ~VM_PAGE_MASK)
 
-#define PFN(x)          ((x) >> VM_PAGE_SHIFT)
+#define PFN(x)          (((x) >> VM_PAGE_SHIFT) & 0xFFFFFFFFFF)
 
 static int can_use_gbpages = 0;
 static pmap_t kernel_pmap;
diff --git a/include/kernel/pmap.h b/include/kernel/pmap.h
index 77e3079..7a6137c 100644
--- a/include/kernel/pmap.h
+++ b/include/kernel/pmap.h
@@ -9,7 +9,6 @@
 #include <stddef.h>
 
 #define PMAP_INVALID ML_PMAP_INVALID
-#define PFN(x)       ((x) >> VM_PAGE_SHIFT)
 
 #ifdef __cplusplus
 extern "C" {