diff --git a/src/object/plane.cpp b/src/object/plane.cpp
index 454654e..4da116e 100644
--- a/src/object/plane.cpp
+++ b/src/object/plane.cpp
@@ -38,7 +38,7 @@ Plane::Plane(std::string& txt) {
 		txt.erase(0, pos + 1);
 		it++;
 	}
-    tmp = txt.substr(0, txt.length - 1);
+    tmp = txt.substr(0, txt.length() - 1);
     this->pts.push_back(new Point(tmp));
 }