diff --git a/blkmaker_jansson.c b/blkmaker_jansson.c
index 5ba24d6..f597bee 100644
--- a/blkmaker_jansson.c
+++ b/blkmaker_jansson.c
@@ -229,7 +229,7 @@ const char *blktmpl_add_jansson(blktemplate_t *tmpl, const json_t *json, time_t
 	if ((v = json_object_get(json, "coinbaseaux")) && json_is_object(v))
 	{
 		tmpl->aux_count = json_object_size(v);
-		tmpl->auxs = malloc(tmpl->aux_count * sizeof(*tmpl->auxs));
+		tmpl->auxs = calloc(tmpl->aux_count, sizeof(*tmpl->auxs));
 		unsigned i = 0;
 		for (void *iter = json_object_iter(v); iter; (iter = json_object_iter_next(v, iter)), ++i)
 		{
@@ -243,7 +243,9 @@ const char *blktmpl_add_jansson(blktemplate_t *tmpl, const json_t *json, time_t
 				.data = malloc(sz),
 				.datasz = sz,
 			};
-			my_hex2bin(tmpl->auxs[i].data, s, sz);
+			if (!my_hex2bin(tmpl->auxs[i].data, s, sz)) {
+				return "Error decoding 'coinbaseaux' data";
+			}
 		}
 	}