diff --git a/src/xml/xml_urdf.cc b/src/xml/xml_urdf.cc
index d6f1b8ed..c69015cd 100644
--- a/src/xml/xml_urdf.cc
+++ b/src/xml/xml_urdf.cc
@@ -255,7 +255,7 @@ void mjXURDF::Body(XMLElement* body_elem) {
       if ((temp = FindSubElem(elem, "material"))) {
         // if color specified - use directly
         if ((temp1 = FindSubElem(temp, "color"))) {
-          ReadAttr(temp1, "rgba", 4, rgba, text);
+          ReadAttr(temp1, "rgba", 4, rgba, text, /*required=*/true);
         }
 
         // otherwise use material table
@@ -332,7 +332,7 @@ void mjXURDF::Joint(XMLElement* joint_elem) {
   double axis[3] = {1, 0, 0};
   Origin(joint_elem, pbody->pos, pbody->quat);
   if ((elem = FindSubElem(joint_elem, "axis"))) {
-    ReadAttr(elem, "xyz", 3, axis, text);
+    ReadAttr(elem, "xyz", 3, axis, text, /*required=*/true);
   }
 
   // create joint (unless fixed)
@@ -626,7 +626,7 @@ void mjXURDF::MakeMaterials(XMLElement* elem) {
       if (FindName(name, urMat) < 0) {
         // add rgba value if available
         if ((color = FindSubElem(elem, "color"))) {
-          ReadAttr(color, "rgba", 4, rgba.val, text);
+          ReadAttr(color, "rgba", 4, rgba.val, text, /*required=*/true);
           AddName(name, urMat);
           urRGBA.push_back(rgba);
         }