diff --git a/lib/nfp-mucus.js b/lib/nfp-mucus.js
index 27e1590..1a8e8a9 100644
--- a/lib/nfp-mucus.js
+++ b/lib/nfp-mucus.js
@@ -1,4 +1,7 @@
 export default function (feeling, texture) {
+
+  if (typeof feeling != 'number' || typeof texture != 'number') return null
+
   const feelingMapping = {
     0: 0,
     1: 1,