diff --git a/include/types/sample.h b/include/types/sample.h
index 956e794..2f21197 100644
--- a/include/types/sample.h
+++ b/include/types/sample.h
@@ -243,6 +243,7 @@
 		       struct sample *smp);       /* process function */
 	unsigned int arg_mask;                    /* arguments (ARG*()) */
 	int (*val_args)(struct arg *arg_p,
+	                struct sample_conv *smp_conv,
 			char **err_msg);          /* argument validation function */
 	unsigned int in_type;                     /* expected input sample type */
 	unsigned int out_type;                    /* output sample type */