diff --git a/src/libopensc/reader-openct.c b/src/libopensc/reader-openct.c
index edd134a9..79f1c64b 100644
--- a/src/libopensc/reader-openct.c
+++ b/src/libopensc/reader-openct.c
@@ -204,7 +204,7 @@ openct_reader_connect(sc_reader_t *reader)
 	}
 
 	rc = ct_card_request(data->h, data->slot, 0, NULL,
-				reader->atr.value, reader->atr.len);
+				reader->atr.value, sizeof(reader->atr.value));
 	if (rc < 0) {
 		sc_debug(reader->ctx, SC_LOG_DEBUG_NORMAL,
 				"openct_reader_connect read failed: %s\n",