diff --git a/ChangeLog b/ChangeLog
index 65826e8..696682d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2019-11-18  NIIBE Yutaka  <gniibe@fsij.org>
+
+	* entry.c: Use chopstx-cortex-m.h.
+	* chopstx.h (CHOPSTX_THREAD_SIZE): Move the definition to ...
+	* chopstx-cortex-m.h (CHOPSTX_THREAD_SIZE): ... here.
+
 2019-10-07  Jeremy Drake  <jeremy@drastrom.science>
 
 	* mcu/usb-st-common.c (usb_lld_init): Move BTABLE initialization
diff --git a/chopstx-cortex-m.h b/chopstx-cortex-m.h
index 36515f6..201639a 100644
--- a/chopstx-cortex-m.h
+++ b/chopstx-cortex-m.h
@@ -10,3 +10,5 @@ struct tcontext {
 };
 
 typedef struct tcontext tcontext_t;
+
+#define CHOPSTX_THREAD_SIZE 64
diff --git a/chopstx.h b/chopstx.h
index d42a071..4b8880c 100644
--- a/chopstx.h
+++ b/chopstx.h
@@ -163,5 +163,3 @@ int chopstx_poll (uint32_t *usec_p, int n,
 		  struct chx_poll_head *const pd_array[]);
 
 int chopstx_conf_idle (int enable_sleep);
-
-#define CHOPSTX_THREAD_SIZE 64
diff --git a/entry.c b/entry.c
index 0576e04..b8f59a0 100644
--- a/entry.c
+++ b/entry.c
@@ -29,7 +29,7 @@
 
 #include <stdint.h>
 #include <stdlib.h>
-#include <chopstx.h>
+#include <chopstx-cortex-m.h>
 
 #include "board.h"