diff --git a/src/core/Buffer.cc b/src/core/Buffer.cc
index 6040b47..1856f58 100644
--- a/src/core/Buffer.cc
+++ b/src/core/Buffer.cc
@@ -229,7 +229,7 @@ size_t Buffer::lines_in_data(size_t offset, size_t length)
     for (size_t i = 0u; i < length; )
     {
         uint8_t bytes;
-        uint32_t c = Encoding::decode(m_encoding, m_gap_buffer->address(offset), &bytes);
+        uint32_t c = Encoding::decode(m_encoding, m_gap_buffer->address(offset + i), &bytes);
         if (c == '\n')
         {
             lines++;