diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 29b6f1ed59ec..b8bbd715fb62 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -694,7 +694,7 @@ static bool handle_in(struct pt_regs *regs, int size, int port)
 		.r13 = PORT_READ,
 		.r14 = port,
 	};
-	u64 mask = GENMASK(BITS_PER_BYTE * size, 0);
+	u64 mask = GENMASK(BITS_PER_BYTE * size - 1, 0);
 	bool success;
 
 	/*
@@ -714,7 +714,7 @@ static bool handle_in(struct pt_regs *regs, int size, int port)
 
 static bool handle_out(struct pt_regs *regs, int size, int port)
 {
-	u64 mask = GENMASK(BITS_PER_BYTE * size, 0);
+	u64 mask = GENMASK(BITS_PER_BYTE * size - 1, 0);
 
 	/*
 	 * Emulate the I/O write via hypercall. More info about ABI can be found