diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index 5701b80..e122ae9 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -94,6 +94,7 @@ inline static void outportw(unsigned short _port, unsigned short _data) {
 /** @brief Write a double word (4 bytes) to an IO port
  *
  * @param _port The port you want to write to
+ * @param _data the 4 byte value you want to write
  */
 inline static void outportl(unsigned short _port, unsigned int _data)
 {