diff --git a/lib/obj2gltf.js b/lib/obj2gltf.js
index 0ceeb37..fe51a20 100644
--- a/lib/obj2gltf.js
+++ b/lib/obj2gltf.js
@@ -63,8 +63,8 @@ function obj2gltf(objPath, options) {
         throw new DeveloperError('Either options.writer or options.outputDirectory must be defined when writing separate resources.');
     }
 
-    if (options.metallicRoughness + options.specularGlossiness > 1) {
-        throw new DeveloperError('Only one material type may be set from [metallicRoughness, specularGlossiness].');
+    if (options.metallicRoughness + options.specularGlossiness + options.unlit > 1) {
+        throw new DeveloperError('Only one material type may be set from [metallicRoughness, specularGlossiness, unlit].');
     }
 
     if (defined(options.overridingTextures.metallicRoughnessOcclusionTexture) && defined(options.overridingTextures.specularGlossinessTexture)) {