diff --git a/include/mbedtls/pk.h b/include/mbedtls/pk.h
index f7fa4d3..36fdea5 100644
--- a/include/mbedtls/pk.h
+++ b/include/mbedtls/pk.h
@@ -475,7 +475,7 @@
  *
  * \return          Maximum size in bytes of a signature made with this key.
  */
-size_t mbedtls_pk_signature_size( const mbedtls_pk_context *ctx );
+size_t mbedtls_pk_get_signature_size( const mbedtls_pk_context *ctx );
 
 /**
  * \brief           Decrypt message (including padding if relevant).
diff --git a/include/mbedtls/pk_info.h b/include/mbedtls/pk_info.h
index d1d95ef..a8b735f 100644
--- a/include/mbedtls/pk_info.h
+++ b/include/mbedtls/pk_info.h
@@ -120,9 +120,11 @@
      * usage restrictions into account. */
     int (*can_do)( const void * ctx, mbedtls_pk_type_t type );
 
-    /** Signature size
+    /** Upper bound of the signature length
      *
-     * mbedtls_pk_signature_size() returns this value.
+     * mbedtls_pk_get_signature_size() returns this value.
+     *
+     * In case of an error, or an unsupported key type, 0 should be returned.
      *
      * Opaque implementations may omit this method if they do not support
      * signature. */