diff --git a/include/polarssl/gcm.h b/include/polarssl/gcm.h
index e4267c6..c2829a0 100644
--- a/include/polarssl/gcm.h
+++ b/include/polarssl/gcm.h
@@ -201,7 +201,7 @@
 /**
  * \brief           Free a GCM context and underlying cipher sub-context
  *
- * \param ctx
+ * \param ctx       GCM context to free
  */
 void gcm_free( gcm_context *ctx );