diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index 1e95d57760cf79becf81c012df564e42ae7122e2..b69f7d428443531ddfb48d9afe0eefaf7d4c22fe 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -230,7 +230,7 @@ bool mmap_address_hint_valid(unsigned long addr, unsigned long len)
 /* Can we access it for direct reading/writing? Must be RAM: */
 int valid_phys_addr_range(phys_addr_t addr, size_t count)
 {
-	return addr + count <= __pa(high_memory);
+	return addr + count - 1 <= __pa(high_memory - 1);
 }
 
 /* Can we access it through mmap? Must be a valid physical address: */