diff --git a/include/ntapi/nt_object.h b/include/ntapi/nt_object.h
index 1dad1d8..995b5f9 100644
--- a/include/ntapi/nt_object.h
+++ b/include/ntapi/nt_object.h
@@ -508,7 +508,7 @@ typedef int32_t __stdcall ntapi_tt_open_ipc_object_directory(
 	__out	void **			hdir,
 	__in	uint32_t		desired_access,
 	__in	const wchar16_t		prefix[6],
-	__in	nt_guid *		guid);
+	__in	const nt_guid *		guid);
 
 typedef int32_t __stdcall ntapi_tt_create_ipc_object_directory_entry(
 	__out	void **			hentry,
@@ -522,14 +522,14 @@ typedef int32_t __stdcall ntapi_tt_create_keyed_object_directory(
 	__out	void **			hdir,
 	__in	uint32_t		desired_access,
 	__in	const wchar16_t		prefix[6],
-	__in	nt_guid *		guid,
+	__in	const nt_guid *		guid,
 	__in	uint32_t		key);
 
 typedef int32_t __stdcall ntapi_tt_open_keyed_object_directory(
 	__out	void **			hdir,
 	__in	uint32_t		desired_access,
 	__in	const wchar16_t		prefix[6],
-	__in	nt_guid *		guid,
+	__in	const nt_guid *		guid,
 	__in	uint32_t		key);
 
 typedef int32_t __stdcall ntapi_tt_create_keyed_object_directory_entry(
diff --git a/include/ntapi/nt_port.h b/include/ntapi/nt_port.h
index 45755e0..4cd330e 100644
--- a/include/ntapi/nt_port.h
+++ b/include/ntapi/nt_port.h
@@ -321,7 +321,7 @@ typedef int32_t __stdcall ntapi_tt_port_guid_from_type(
 typedef int32_t __stdcall ntapi_tt_port_type_from_guid(
 	__out	nt_port_type *		type,
 	__out	nt_port_subtype *	subtype,
-	__in	nt_guid *		guid);
+	__in	const nt_guid *		guid);
 
 
 typedef int32_t __stdcall	ntapi_tt_port_generate_keys(
diff --git a/src/object/ntapi_tt_keyed_object_directory.c b/src/object/ntapi_tt_keyed_object_directory.c
index b2919f0..c744326 100644
--- a/src/object/ntapi_tt_keyed_object_directory.c
+++ b/src/object/ntapi_tt_keyed_object_directory.c
@@ -23,7 +23,7 @@ static int32_t __stdcall __tt_create_ipc_object_directory(
 	__out	void **			hdir,
 	__in	uint32_t		desired_access,
 	__in	const wchar16_t		prefix[6],
-	__in	nt_guid *		guid)
+	__in	const nt_guid *		guid)
 {
 	int32_t			status;
 	nt_ipc_objdir_name	objdir_name;
@@ -78,7 +78,7 @@ static int32_t __stdcall __tt_create_keyed_object_directory(
 	__out	void **			hdir,
 	__in	uint32_t		desired_access,
 	__in	const wchar16_t		prefix[6],
-	__in	nt_guid *		guid,
+	__in	const nt_guid *		guid,
 	__in	uint32_t		key,
 	__in	objdir_open_fn *	openfn)
 {
@@ -178,7 +178,7 @@ int32_t __stdcall __ntapi_tt_open_ipc_object_directory(
 	__out	void **			hdir,
 	__in	uint32_t		desired_access,
 	__in	const wchar16_t		prefix[6],
-	__in	nt_guid *		guid)
+	__in	const nt_guid *		guid)
 {
 	return __tt_create_ipc_object_directory(
 		hdir,desired_access,
@@ -202,7 +202,7 @@ int32_t __stdcall __ntapi_tt_create_keyed_object_directory(
 	__out	void **			hdir,
 	__in	uint32_t		desired_access,
 	__in	const wchar16_t		prefix[6],
-	__in	nt_guid *		guid,
+	__in	const nt_guid *		guid,
 	__in	uint32_t		key)
 {
 	return __tt_create_keyed_object_directory(
@@ -215,7 +215,7 @@ int32_t __stdcall __ntapi_tt_open_keyed_object_directory(
 	__out	void **			hdir,
 	__in	uint32_t		desired_access,
 	__in	const wchar16_t		prefix[6],
-	__in	nt_guid *		guid,
+	__in	const nt_guid *		guid,
 	__in	uint32_t		key)
 {
 	return __tt_create_keyed_object_directory(
diff --git a/src/port/ntapi_port_name_helper.c b/src/port/ntapi_port_name_helper.c
index 8c811fa..e55ffba 100644
--- a/src/port/ntapi_port_name_helper.c
+++ b/src/port/ntapi_port_name_helper.c
@@ -57,7 +57,7 @@ int32_t __stdcall __ntapi_tt_port_guid_from_type(
 int32_t __stdcall __ntapi_tt_port_type_from_guid(
 	__out	nt_port_type *		type,
 	__out	nt_port_subtype *	subtype,
-	__in	nt_guid *		guid)
+	__in	const nt_guid *		guid)
 {
 	int		itype;
 	int		isubtype;