diff --git a/amixer/amixer.c b/amixer/amixer.c
index f822ba3..d4a59e6 100644
--- a/amixer/amixer.c
+++ b/amixer/amixer.c
@@ -1486,7 +1486,7 @@ int main(int argc, char *argv[])
 			break;
 		case 'D':
 		case HELPID_DEVICE:
-			strncpy(card, optarg, sizeof(card-1));
+			strncpy(card, optarg, sizeof(card)-1);
 			card[sizeof(card)-1] = '\0';
 			break;
 		case 'q':