diff --git a/Include/sysmodule.h b/Include/sysmodule.h
index 3ff01bd..8ea7eb1 100644
--- a/Include/sysmodule.h
+++ b/Include/sysmodule.h
@@ -7,10 +7,10 @@
 extern "C" {
 #endif
 
-PyAPI_FUNC(PyObject *) PySys_GetObject(char *);
-PyAPI_FUNC(int) PySys_SetObject(char *, PyObject *);
+PyAPI_FUNC(PyObject *) PySys_GetObject(const char *);
+PyAPI_FUNC(int) PySys_SetObject(const char *, PyObject *);
 PyAPI_FUNC(void) PySys_SetArgv(int, char **);
-PyAPI_FUNC(void) PySys_SetPath(char *);
+PyAPI_FUNC(void) PySys_SetPath(const char *);
 
 PyAPI_FUNC(void) PySys_WriteStdout(const char *format, ...)
 			Py_GCC_ATTRIBUTE((format(printf, 1, 2)));
@@ -21,7 +21,7 @@
 PyAPI_DATA(int) _PySys_CheckInterval;
 
 PyAPI_FUNC(void) PySys_ResetWarnOptions(void);
-PyAPI_FUNC(void) PySys_AddWarnOption(char *);
+PyAPI_FUNC(void) PySys_AddWarnOption(const char *);
 
 #ifdef __cplusplus
 }