diff --git a/include/polarssl/ecp.h b/include/polarssl/ecp.h
index 94618e7..dec4e0a 100644
--- a/include/polarssl/ecp.h
+++ b/include/polarssl/ecp.h
@@ -450,6 +450,7 @@
 
 /**
  * \brief           Multiplication by an integer: R = m * P
+ *                  (Not thread-safe to use same group in multiple threads)
  *
  * \param grp       ECP group
  * \param R         Destination point