correction for #316
diff --git a/src/lib_json/json_tool.h b/src/lib_json/json_tool.h
index 2de0d83..e65e51b 100644
--- a/src/lib_json/json_tool.h
+++ b/src/lib_json/json_tool.h
@@ -43,7 +43,7 @@
   return result;
 }
 
-/// Returns true if ch is a control character (in range [0,32]).
+/// Returns true if ch is a control character (in range [1,31]).
 static inline bool isControlCharacter(char ch) { return ch > 0 && ch <= 0x1F; }
 
 enum {