diff --git a/filesystem/dfs/include/dfs_util.h b/filesystem/dfs/include/dfs_util.h
index 0b50ccbca6280a39c35d81b5078bcccdc354a045..41ba8f2d3625cb682a5ca0f01d28537a701bacb0 100644
--- a/filesystem/dfs/include/dfs_util.h
+++ b/filesystem/dfs/include/dfs_util.h
@@ -28,6 +28,7 @@ int str_is_prefix(const char* prefix, const char* str);
 #if !defined(RT_USING_MINILIBC) && !defined(RT_USING_NEWLIB)
 char *strrchr(const char *t, int c);
 #if defined (__ARMCC_VERSION) && (__ARMCC_VERSION / 10000 < 35)
+#include <stddef.h>
 int strncasecmp(const char* s1, const char* s2, size_t len);
 #endif /* end of __ARMCC_VERSION */
 #endif