diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index ebbf80d..f63c308 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -9,6 +9,8 @@ and this project adheres to `Semantic Versioning <https://semver.org/spec/v2.0.0
 `Unreleased`_
 -------------
 
+- Fix bug in SensirionShdlcTxFrame::begin that caused communication timeouts.
+
 `0.7.2`_ 2025-11-04
 -------------------
 
diff --git a/src/SensirionShdlcTxFrame.cpp b/src/SensirionShdlcTxFrame.cpp
index 693c030..42cb1e4 100644
--- a/src/SensirionShdlcTxFrame.cpp
+++ b/src/SensirionShdlcTxFrame.cpp
@@ -39,7 +39,7 @@
 uint16_t SensirionShdlcTxFrame::begin(uint8_t command, uint8_t address,
                                       uint8_t dataLength) {
     _index = 0;  // sets the index to point towards the start of the buffer.
-    _buffer[_index] = 0x7e;
+    _buffer[_index++] = 0x7e;
     uint16_t error = addUInt8(address);
     error |= addUInt8(command);
     error |= addUInt8(dataLength);