diff --git a/src/cashaddrenc.cpp b/src/cashaddrenc.cpp
--- a/src/cashaddrenc.cpp
+++ b/src/cashaddrenc.cpp
@@ -26,7 +26,13 @@
 template <class T>
 std::vector<uint8_t> PackAddrData(const T &id, uint8_t type,
                                   size_t expectedSize) {
-    std::vector<uint8_t> data = {uint8_t(type << 3)};
+    uint8_t version_byte = uint8_t(type << 3);
+    uint8_t encoded_size = (id.size() - 20) / 4;
+    assert((id.size() - 20) % 4 == 0);
+    assert(encoded_size >= 0 && encoded_size < 8);
+
+    version_byte |= encoded_size;
+    std::vector<uint8_t> data = {version_byte};
     data.insert(data.end(), id.begin(), id.end());
 
     std::vector<uint8_t> converted;