diff --git a/lib/interpolate.c b/lib/interpolate.c
index a9c009b..65ef2aa 100644
--- a/lib/interpolate.c
+++ b/lib/interpolate.c
@@ -74,6 +74,9 @@ switch (s1->type) {
 		gray_interpolate (s1, s2, d, coef);	break;
 	case FIMG_TYPE_RGB:
 		rgb_interpolate  (s1, s2, d, coef);	break;
+	case FIMG_TYPE_RGBA:
+		fprintf(stderr, "WTF?\n");
+		return -18;
 	default:
 		fprintf(stderr, "%s, %d is a bad type\n", __func__, s1->type);
 		return -18;