diff --git a/src/engine/executors/aggregate-executor.js b/src/engine/executors/aggregate-executor.js
index 9c50c163..d95ccc33 100644
--- a/src/engine/executors/aggregate-executor.js
+++ b/src/engine/executors/aggregate-executor.js
@@ -52,10 +52,6 @@ class AggregateExecutor {
       if ('having' in query) {
         iterator = this._executeHaving(iterator, query.having, options)
       }
-      // finally, apply each aggregate operation over the groups
-      iterator = query.aggregates.reduce((iter, agg) => {
-        return this._executeAggregate(iter, agg, options)
-      }, iterator)
       return iterator
     }
     return source
diff --git a/src/engine/plan-builder.js b/src/engine/plan-builder.js
index 354e6c80..ba3b6a18 100644
--- a/src/engine/plan-builder.js
+++ b/src/engine/plan-builder.js
@@ -26,6 +26,7 @@ SOFTWARE.
 
 const { Parser } = require('sparqljs')
 const { single } = require('asynciterator')
+const AggregateOperator = require('../operators/aggregates/agg-operator.js')
 const BindOperator = require('../operators/bind-operator.js')
 const UnionOperator = require('../operators/union-operator.js')
 const DistinctIterator = require('../operators/distinct-operator.js')
@@ -202,7 +203,7 @@ class PlanBuilder {
     }
 
     // Parse query variable to separate projection & aggregate variables
-    if (query.variables != null) {
+    if ('variables' in query) {
       const [projection, aggregates] = _.partition(query.variables, v => _.isString(v))
       // add aggregates variables to projection variables
       query.variables = projection.concat(aggregates.map(agg => agg.variable))
@@ -212,6 +213,13 @@ class PlanBuilder {
     // Handles Aggregates
     graphIterator = this._aggExecutor.buildIterator(graphIterator, query, options)
 
+    // Handles transformers
+    if ('aggregates' in query) {
+      graphIterator = query.aggregates.reduce((iter, agg) => {
+        return new AggregateOperator(iter, agg, options)
+      }, graphIterator)
+    }
+
     // Handles ORDER BY
     if ('order' in query) {
       graphIterator = new OrderByOperator(graphIterator, query.order, options)
diff --git a/src/operators/expressions/sparql-expression.js b/src/operators/expressions/sparql-expression.js
index b2cf1aee..32e88a5f 100644
--- a/src/operators/expressions/sparql-expression.js
+++ b/src/operators/expressions/sparql-expression.js
@@ -75,7 +75,12 @@ class SPARQLExpression {
         throw new Error(`Unsupported SPARQL aggregation: ${expression.aggregation}`)
       }
       const aggregation = aggregates[expression.aggregation]
-      return bindings => aggregation(expression.expression, bindings['__aggregate'], expression.separator)
+      return bindings => {
+        if ('__aggregate' in bindings) {
+          return aggregation(expression.expression, bindings['__aggregate'], expression.separator)
+        }
+        return bindings
+      }
     }
     throw new Error(`Unsupported SPARQL operation type found: ${expression.type}`)
   }