diff --git a/CHANGELOG.md b/CHANGELOG.md
index 06661a37..a6b71ade 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,3 +16,4 @@ HEAD
 * Always store `serialized("string")` by copy (#1915)
 * Remove the zero-copy mode of `deserializeJson()` and `deserializeMsgPack()`
 * Fix double lookup in `to<JsonVariant>()`
+* Fix double call to `size()` in `serializeMsgPack()`
\ No newline at end of file
diff --git a/src/ArduinoJson/MsgPack/MsgPackSerializer.hpp b/src/ArduinoJson/MsgPack/MsgPackSerializer.hpp
index 0b727ee8..374d3172 100644
--- a/src/ArduinoJson/MsgPack/MsgPackSerializer.hpp
+++ b/src/ArduinoJson/MsgPack/MsgPackSerializer.hpp
@@ -47,7 +47,7 @@ class MsgPackSerializer : public Visitor<size_t> {
   size_t visitArray(const ArrayData& array) {
     size_t n = array.size();
     if (n < 0x10) {
-      writeByte(uint8_t(0x90 + array.size()));
+      writeByte(uint8_t(0x90 + n));
     } else if (n < 0x10000) {
       writeByte(0xDC);
       writeInteger(uint16_t(n));