diff --git a/autotests/aztecbarcodetest.cpp b/autotests/aztecbarcodetest.cpp
--- a/autotests/aztecbarcodetest.cpp
+++ b/autotests/aztecbarcodetest.cpp
@@ -123,9 +123,12 @@
 
         BitVector in, out;
         QTest::newRow("emtpy") << in << out << 4;
-        in.appendMSB(0x3, 2); out.appendMSB(0xf, 4);
+        in.appendMSB(0x2, 2); out.appendMSB(0xB, 4);
         QTest::newRow("pad only") << in << out << 4;
         in.clear(); out.clear();
+        in.appendMSB(0x3, 2); out.appendMSB(0xE, 4);
+        QTest::newRow("pad only inverted") << in << out << 4;
+        in.clear(); out.clear();
         in.appendMSB(0xe0, 8); out.appendMSB(0xe13, 12);
         QTest::newRow("stuff and pad") << in << out << 4;
         in.clear(); out.clear();
diff --git a/src/lib/aztecbarcode.cpp b/src/lib/aztecbarcode.cpp
--- a/src/lib/aztecbarcode.cpp
+++ b/src/lib/aztecbarcode.cpp
@@ -576,9 +576,24 @@
         res.appendBit(input.at(i++));
     }
 
-    // pad to nearest code word boundary
+    // check if we are code word aligned already
+    const auto trailingBits = res.size() % codeWordSize;
+    if (!trailingBits) { // nothing to pad
+        return res;
+    }
+
+    // pad with ones to nearest code word boundary
+    // last bit has to be zero if we'd otherwise would have all ones though
+    bool allOnes = true;
+    for (int i = res.size() - trailingBits; i < res.size(); ++i) {
+        allOnes &= res.at(i);
+    }
     while (res.size() % codeWordSize) {
-        res.appendBit(true);
+        if ((res.size() % codeWordSize) == (codeWordSize - 1)) {
+            res.appendBit(allOnes ? false : true);
+        } else {
+            res.appendBit(true);
+        }
     }
 
     return res;