diff --git a/force-app/main/default/classes/SOQL.cls b/force-app/main/default/classes/SOQL.cls
index cb29732..0044e1e 100644
--- a/force-app/main/default/classes/SOQL.cls
+++ b/force-app/main/default/classes/SOQL.cls
@@ -547,6 +547,7 @@ public virtual inherited sharing class SOQL implements Queryable {
 
     public Set<String> toValuesOf(SObjectField fieldToExtract) {
         // https://salesforce.stackexchange.com/questions/393308/get-a-list-of-one-column-from-a-soql-result
+        builder.fields.clearAllFields(); // other fields not needed
         return new Map<String, SObject>(with(fieldToExtract, 'Id').groupBy(fieldToExtract).toAggregated()).keySet();
     }
 
diff --git a/force-app/main/default/classes/SOQL_Test.cls b/force-app/main/default/classes/SOQL_Test.cls
index 4f25d74..eff7023 100644
--- a/force-app/main/default/classes/SOQL_Test.cls
+++ b/force-app/main/default/classes/SOQL_Test.cls
@@ -1348,6 +1348,19 @@ private class SOQL_Test {
         );
     }
 
+    @IsTest
+    static void groupByWithDefaultFields() {
+        // Test
+        String soql = SOQL.of(Lead.SObjectType)
+            .with(Lead.FirstName, Lead.LastName, Lead.Email)
+            .with(Lead.LeadSource)
+            .groupBy(Lead.LeadSource)
+            .toString();
+
+        // Verify
+        Assert.areEqual('SELECT LeadSource FROM Lead GROUP BY LeadSource', soql);
+    }
+
     @IsTest
     static void orderByString() {
         // Test