diff --git a/source/MaterialXCore/Element.cpp b/source/MaterialXCore/Element.cpp
index 18d028efd3..5131dc8070 100644
--- a/source/MaterialXCore/Element.cpp
+++ b/source/MaterialXCore/Element.cpp
@@ -168,7 +168,7 @@ void Element::setChildIndex(const string& name, int index)
         return;
     }
 
-    if (index < 0 || index > (int) _childOrder.size())
+    if (index < 0 || index >= (int) _childOrder.size())
     {
         throw Exception("Invalid child index");
     }
diff --git a/source/MaterialXTest/MaterialXCore/Element.cpp b/source/MaterialXTest/MaterialXCore/Element.cpp
index fc4939a74f..3865934ccb 100644
--- a/source/MaterialXTest/MaterialXCore/Element.cpp
+++ b/source/MaterialXTest/MaterialXCore/Element.cpp
@@ -54,6 +54,9 @@ TEST_CASE("Element", "[element]")
     REQUIRE(*doc2 != *doc);
     doc2->setChildIndex("elem1", doc2->getChildIndex("elem2"));
     REQUIRE(*doc2 == *doc);
+    REQUIRE_THROWS_AS(doc2->setChildIndex("elem1", -100), mx::Exception);
+    REQUIRE_THROWS_AS(doc2->setChildIndex("elem1", -1), mx::Exception);
+    REQUIRE_THROWS_AS(doc2->setChildIndex("elem1", 2), mx::Exception);
     REQUIRE_THROWS_AS(doc2->setChildIndex("elem1", 100), mx::Exception);
     REQUIRE(*doc2 == *doc);