diff --git a/components/libc/compilers/common/extension/sys/types.h b/components/libc/compilers/common/extension/sys/types.h
index 71907a65dbd2715c027a7648f4c9a5ff30a7e714..cae4d4adcd6e04fc548d759fa63ebf2d77e51028 100644
--- a/components/libc/compilers/common/extension/sys/types.h
+++ b/components/libc/compilers/common/extension/sys/types.h
@@ -27,11 +27,7 @@ typedef unsigned short   uid_t;
 typedef unsigned short   gid_t;
 typedef signed long      off_t;
 typedef int              mode_t;
-#ifndef ARCH_CPU_64BIT
-typedef signed int       ssize_t;       /* Used for a count of bytes or an error indication. */
-#else
-typedef long signed int  ssize_t;       /* Used for a count of bytes or an error indication. */
-#endif
+typedef signed long      ssize_t;       /* Used for a count of bytes or an error indication. */
 typedef unsigned long    __timer_t;
 typedef __timer_t        timer_t;
 typedef long             suseconds_t;   /* microseconds. */
diff --git a/include/rtdef.h b/include/rtdef.h
index 4f519e6dc3231417e69b0bae8fb8cce1d954edc1..89ac9edf6eeb61db0c37285832b385bc86c6c3ca 100644
--- a/include/rtdef.h
+++ b/include/rtdef.h
@@ -45,6 +45,7 @@
  * 2022-04-21     THEWON       add macro RT_VERSION_CHECK
  * 2022-06-29     Meco Man     add RT_USING_LIBC and standard libc headers
  * 2022-08-16     Meco Man     change version number to v5.0.0
+ * 2022-09-12     Meco Man     define rt_ssize_t
  */
 
 #ifndef __RT_DEF_H__
@@ -55,6 +56,7 @@
 #include <stdint.h>
 #include <stddef.h>
 #include <stdarg.h>
+#include <sys/types.h>
 #endif /* RT_USING_LIBC */
 
 #ifdef __cplusplus
@@ -80,6 +82,10 @@ extern "C" {
 
 
 /* RT-Thread basic data type definitions */
+typedef int                             rt_bool_t;      /**< boolean type */
+typedef signed long                     rt_base_t;      /**< Nbit CPU related date type */
+typedef unsigned long                   rt_ubase_t;     /**< Nbit unsigned CPU related data type */
+
 #ifndef RT_USING_ARCH_DATA_TYPE
 #ifdef RT_USING_LIBC
 typedef int8_t                          rt_int8_t;      /**<  8bit integer type */
@@ -91,7 +97,7 @@ typedef uint32_t                        rt_uint32_t;    /**< 32bit unsigned inte
 typedef int64_t                         rt_int64_t;     /**< 64bit integer type */
 typedef uint64_t                        rt_uint64_t;    /**< 64bit unsigned integer type */
 typedef size_t                          rt_size_t;      /**< Type for size number */
-
+typedef ssize_t                         rt_ssize_t;     /**< Used for a count of bytes or an error indication */
 #else
 typedef signed   char                   rt_int8_t;      /**<  8bit integer type */
 typedef signed   short                  rt_int16_t;     /**< 16bit integer type */
@@ -99,23 +105,18 @@ typedef signed   int                    rt_int32_t;     /**< 32bit integer type
 typedef unsigned char                   rt_uint8_t;     /**<  8bit unsigned integer type */
 typedef unsigned short                  rt_uint16_t;    /**< 16bit unsigned integer type */
 typedef unsigned int                    rt_uint32_t;    /**< 32bit unsigned integer type */
-
 #ifdef ARCH_CPU_64BIT
 typedef signed long                     rt_int64_t;     /**< 64bit integer type */
 typedef unsigned long                   rt_uint64_t;    /**< 64bit unsigned integer type */
-typedef unsigned long                   rt_size_t;      /**< Type for size number */
 #else
 typedef signed long long                rt_int64_t;     /**< 64bit integer type */
 typedef unsigned long long              rt_uint64_t;    /**< 64bit unsigned integer type */
-typedef unsigned int                    rt_size_t;      /**< Type for size number */
 #endif /* ARCH_CPU_64BIT */
+typedef rt_ubase_t                      rt_size_t;      /**< Type for size number */
+typedef rt_base_t                       rt_ssize_t;     /**< Used for a count of bytes or an error indication */
 #endif /* RT_USING_LIBC */
 #endif /* RT_USING_ARCH_DATA_TYPE */
 
-typedef int                             rt_bool_t;      /**< boolean type */
-typedef long                            rt_base_t;      /**< Nbit CPU related date type */
-typedef unsigned long                   rt_ubase_t;     /**< Nbit unsigned CPU related data type */
-
 typedef rt_base_t                       rt_err_t;       /**< Type for error number */
 typedef rt_uint32_t                     rt_time_t;      /**< Type for time stamp */
 typedef rt_uint32_t                     rt_tick_t;      /**< Type for tick count */