diff --git a/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php b/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
index 2e85c6314e49dd994e0eef2613434968edf56f14..3c6d4c49a38facf7a45d7d7998bc9a74851b33ad 100644
--- a/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
+++ b/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
@@ -234,6 +234,7 @@ protected function initializeIterator() {
       //      OR above high water).
       $conditions = $this->query->orConditionGroup();
       $condition_added = FALSE;
+      $added_fields = [];
       if (empty($this->configuration['ignore_map']) && $this->mapJoinable()) {
         // Build the join to the map table. Because the source key could have
         // multiple fields, we need to build things up.
@@ -259,14 +260,17 @@ protected function initializeIterator() {
         for ($count = 1; $count <= $n; $count++) {
           $map_key = 'sourceid' . $count;
           $this->query->addField($alias, $map_key, "migrate_map_$map_key");
+          $added_fields[] = "$alias.$map_key";
         }
         if ($n = count($this->migration->getDestinationIds())) {
           for ($count = 1; $count <= $n; $count++) {
             $map_key = 'destid' . $count++;
             $this->query->addField($alias, $map_key, "migrate_map_$map_key");
+            $added_fields[] = "$alias.$map_key";
           }
         }
         $this->query->addField($alias, 'source_row_status', 'migrate_map_source_row_status');
+        $added_fields[] = "$alias.source_row_status";
       }
       // 2. If we are using high water marks, also include rows above the mark.
       //    But, include all rows if the high water mark is not set.
@@ -279,6 +283,15 @@ protected function initializeIterator() {
       if ($condition_added) {
         $this->query->condition($conditions);
       }
+      // If the query has a group by, our added fields need it too, to keep the
+      // query valid.
+      // @see https://dev.mysql.com/doc/refman/5.7/en/group-by-handling.html
+      $group_by = $this->query->getGroupBy();
+      if ($group_by && $added_fields) {
+        foreach ($added_fields as $added_field) {
+          $this->query->groupBy($added_field);
+        }
+      }
     }
 
     // Download data in batches for performance.
diff --git a/core/modules/migrate/tests/modules/migrate_high_water_test/src/Plugin/migrate/source/HighWaterTest.php b/core/modules/migrate/tests/modules/migrate_high_water_test/src/Plugin/migrate/source/HighWaterTest.php
index 83767211830ebe6f474bc5a785c7bf08893ec7b8..601bbd942b785d2eb8628586959205b84e75b8e3 100644
--- a/core/modules/migrate/tests/modules/migrate_high_water_test/src/Plugin/migrate/source/HighWaterTest.php
+++ b/core/modules/migrate/tests/modules/migrate_high_water_test/src/Plugin/migrate/source/HighWaterTest.php
@@ -17,9 +17,13 @@ class HighWaterTest extends SqlBase {
    * {@inheritdoc}
    */
   public function query() {
+    $field_names = array_keys($this->fields());
     $query = $this
       ->select('high_water_node', 'm')
-      ->fields('m', array_keys($this->fields()));
+      ->fields('m', $field_names);
+    foreach ($field_names as $field_name) {
+      $query->groupBy($field_name);
+    }
     return $query;
   }