diff --git a/include/strings.h b/include/strings.h
index 6730937a6..a5ac550a1 100755
--- a/include/strings.h
+++ b/include/strings.h
@@ -58,7 +58,7 @@ public:
       operator const char*() const { return (const char*)_str; }  // *(TString) -> _str
   char& operator[](int i)                                     // TString[i] -> _str[i]
   { 
-    CHECKD(i >= 0 && i < _size, "Bad string subscript: ", i);
+    CHECKD(i >= 0 && i <= _size, "Bad string subscript: ", i);
     return _str[i]; 
   }