diff --git a/include/mbedtls/pk.h b/include/mbedtls/pk.h
index 6289e8e..6c4ca38 100644
--- a/include/mbedtls/pk.h
+++ b/include/mbedtls/pk.h
@@ -430,7 +430,8 @@
  *
  * \return          1 if the context can do operations on the given type.
  * \return          0 if the context cannot do the operations on the given
- *                  type. This is always the case for a context that has
+ *                  type, or for non-allowed algorithms and usage flags.
+ *                  This is always the case for a context that has
  *                  been initialized but not set up, or that has been
  *                  cleared with mbedtls_pk_free().
  */