diff --git a/cpp/QrCode.cpp b/cpp/QrCode.cpp
index deac175..0bfbd35 100644
--- a/cpp/QrCode.cpp
+++ b/cpp/QrCode.cpp
@@ -348,7 +348,7 @@ void qrcodegen::QrCode::drawCodewords(const std::vector<uint8_t> &data) {
 				bool upwards = ((right & 2) == 0) ^ (x < 6);
 				int y = upwards ? size - 1 - vert : vert;  // Actual y coordinate
 				if (!isFunction.at(y).at(x) && i < data.size() * 8) {
-					modules.at(y).at(x) = ((data[i >> 3] >> (7 - (i & 7))) & 1) != 0;
+					modules.at(y).at(x) = ((data.at(i >> 3) >> (7 - (i & 7))) & 1) != 0;
 					i++;
 				}
 			}
diff --git a/javascript/qrcodegen.js b/javascript/qrcodegen.js
index 5b2af31..ceea27c 100644
--- a/javascript/qrcodegen.js
+++ b/javascript/qrcodegen.js
@@ -86,6 +86,8 @@ var qrcodegen = new function() {
 			if (version < 1 || version > 40)
 				throw "Version value out of range";
 		} else if (initData instanceof qrcodegen.QrCode) {
+			if (version != undefined || errCorLvl != undefined)
+				throw "Values must be undefined";
 			version = initData.version;
 			errCorLvl = initData.errorCorrectionLevel;
 		} else
diff --git a/python/qrcodegen.py b/python/qrcodegen.py
index 0464c0f..8dd0616 100644
--- a/python/qrcodegen.py
+++ b/python/qrcodegen.py
@@ -158,6 +158,8 @@ class QrCode(object):
 			if not isinstance(errcorlvl, QrCode.Ecc):
 				raise TypeError("QrCode.Ecc expected")
 		elif qrcode is not None and datacodewords is None:
+			if version is not None or errcorlvl is not None:
+				raise ValueError("Values must be None")
 			version = qrcode._version
 			errcorlvl = qrcode._errcorlvl
 		else: