diff --git a/app/imports/parser/parseTree/IndexNode.js b/app/imports/parser/parseTree/IndexNode.js
index 850ff088..fdd6c6c6 100644
--- a/app/imports/parser/parseTree/IndexNode.js
+++ b/app/imports/parser/parseTree/IndexNode.js
@@ -1,4 +1,6 @@
 import ParseNode from '/imports/parser/parseTree/ParseNode.js';
+import ArrayNode from '/imports/parser/parseTree/ArrayNode.js';
+import ErrorNode from '/imports/parser/parseTree/ErrorNode.js';
 
 export default class IndexNode extends ParseNode {
   constructor({array, index}) {
@@ -8,16 +10,42 @@ export default class IndexNode extends ParseNode {
   }
   resolve(fn, scope, context){
     let index = this.index[fn](scope, context);
-    if (index.isInteger){
-      let selection = this.array.values[index.value - 1];
+    let array = this.array[fn](scope, context);
+
+    if (index.isInteger && array instanceof ArrayNode){
+      if (index.value < 1 || index.value > array.values.length){
+        if (context){
+          context.storeError({
+            type: 'warning',
+            message: `Index of ${index.value} is out of range for an array` +
+              ` of length ${array.values.length}`,
+          });
+        }
+      }
+      let selection = array.values[index.value - 1];
       if (selection){
         let result = selection[fn](scope, context);
         return result;
       }
+    } else if (fn === 'reduce'){
+      if (!(array instanceof ArrayNode)){
+        return new ErrorNode({
+          node: this,
+          error: 'Can not get the index of a non-array node: ' +
+            this.array.toString() + ' = ' + array.toString(),
+          context,
+        });
+      } else if (!index.isInteger){
+        return new ErrorNode({
+          node: this,
+          error: array.toString() + ' is not an integer index of the array',
+          context,
+        });
+      }
     }
     return new IndexNode({
       index,
-      array: this.array[fn](scope, context),
+      array,
       previousNodes: [this],
     });
   }
diff --git a/app/imports/parser/parseTree/ParenthesisNode.js b/app/imports/parser/parseTree/ParenthesisNode.js
index eda6038f..db6b5e14 100644
--- a/app/imports/parser/parseTree/ParenthesisNode.js
+++ b/app/imports/parser/parseTree/ParenthesisNode.js
@@ -8,6 +8,7 @@ export default class ParenthesisNode extends ParseNode {
   resolve(fn, scope, context){
     let content = this.content[fn](scope, context);
     if (
+      fn === 'reduce' ||
       content.constructor.name === 'ConstantNode' ||
       content.constructor.name === 'ErrorNode'
     ){