diff --git a/src/ORM/Map.php b/src/ORM/Map.php
index 6bcd68494..a79177f8d 100644
--- a/src/ORM/Map.php
+++ b/src/ORM/Map.php
@@ -260,13 +260,48 @@ class Map implements ArrayAccess, Countable, IteratorAggregate
     #[\ReturnTypeWillChange]
     public function getIterator()
     {
-        return new Map_Iterator(
-            $this->list->getIterator(),
-            $this->keyField,
-            $this->valueField,
-            $this->firstItems,
-            $this->lastItems
-        );
+        $keyField = $this->keyField;
+        $valueField = $this->valueField;
+
+        foreach($this->firstItems as $k => $v) {
+            yield $k => $v;
+        }
+
+        foreach($this->list as $record) {
+            if(isset($this->firstItems[$record->$keyField])) {
+                continue;
+            }
+            if(isset($this->lastItems[$record->$keyField])) {
+                continue;
+            }
+            yield $this->extractValue($record, $this->keyField) => $this->extractValue($record, $this->valueField);
+        }
+
+        foreach($this->lastItems as $k => $v) {
+            yield $k => $v;
+        }
+    }
+
+    /**
+     * Extracts a value from an item in the list, where the item is either an
+     * object or array.
+     *
+     * @param  array|object $item
+     * @param  string $key
+     * @return mixed
+     */
+    protected function extractValue($item, $key)
+    {
+        if (is_object($item)) {
+            if (method_exists($item, 'hasMethod') && $item->hasMethod($key)) {
+                return $item->{$key}();
+            }
+            return $item->{$key};
+        } else {
+            if (array_key_exists($key, $item)) {
+                return $item[$key];
+            }
+        }
     }
 
     /**
diff --git a/src/ORM/Map_Iterator.php b/src/ORM/Map_Iterator.php
deleted file mode 100644
index d645ca07d..000000000
--- a/src/ORM/Map_Iterator.php
+++ /dev/null
@@ -1,200 +0,0 @@
-<?php
-
-namespace SilverStripe\ORM;
-
-use Iterator;
-
-/**
- * Builds a map iterator around an Iterator.  Called by Map
- */
-class Map_Iterator implements Iterator
-{
-
-    /**
-     * @var Iterator
-     **/
-    protected $items;
-
-    protected $keyField, $titleField;
-
-    protected $firstItemIdx = 0;
-
-    protected $endItemIdx;
-
-    protected $firstItems = [];
-    protected $lastItems = [];
-
-    protected $excludedItems = [];
-
-    /**
-     * @param Iterator $items The iterator to build this map from
-     * @param string $keyField The field to use for the keys
-     * @param string $titleField The field to use for the values
-     * @param array $firstItems An optional map of items to show first
-     * @param array $lastItems An optional map of items to show last
-     */
-    public function __construct(Iterator $items, $keyField, $titleField, $firstItems = null, $lastItems = null)
-    {
-        $this->items = $items;
-        $this->keyField = $keyField;
-        $this->titleField = $titleField;
-        $this->endItemIdx = null;
-
-        if ($firstItems) {
-            foreach ($firstItems as $k => $v) {
-                $this->firstItems[] = [$k, $v];
-                $this->excludedItems[] = $k;
-            }
-        }
-
-        if ($lastItems) {
-            foreach ($lastItems as $k => $v) {
-                $this->lastItems[] = [$k, $v];
-                $this->excludedItems[] = $k;
-            }
-        }
-    }
-
-    /**
-     * Rewind the Iterator to the first element.
-     *
-     * @return mixed
-     */
-    #[\ReturnTypeWillChange]
-    public function rewind()
-    {
-        $this->firstItemIdx = 0;
-        $this->endItemIdx = null;
-
-        $rewoundItem = $this->items->rewind();
-
-        if (isset($this->firstItems[$this->firstItemIdx])) {
-            return $this->firstItems[$this->firstItemIdx][1];
-        } else {
-            if ($rewoundItem) {
-                return $this->extractValue($rewoundItem, $this->titleField);
-            } else {
-                if (!$this->items->valid() && $this->lastItems) {
-                    $this->endItemIdx = 0;
-
-                    return $this->lastItems[0][1];
-                }
-            }
-        }
-    }
-
-    /**
-     * Return the current element.
-     *
-     * @return mixed
-     */
-    #[\ReturnTypeWillChange]
-    public function current()
-    {
-        if (($this->endItemIdx !== null) && isset($this->lastItems[$this->endItemIdx])) {
-            return $this->lastItems[$this->endItemIdx][1];
-        } else {
-            if (isset($this->firstItems[$this->firstItemIdx])) {
-                return $this->firstItems[$this->firstItemIdx][1];
-            }
-        }
-        return $this->extractValue($this->items->current(), $this->titleField);
-    }
-
-    /**
-     * Extracts a value from an item in the list, where the item is either an
-     * object or array.
-     *
-     * @param  array|object $item
-     * @param  string $key
-     * @return mixed
-     */
-    protected function extractValue($item, $key)
-    {
-        if (is_object($item)) {
-            if (method_exists($item, 'hasMethod') && $item->hasMethod($key)) {
-                return $item->{$key}();
-            }
-            return $item->{$key};
-        } else {
-            if (array_key_exists($key, $item ?? [])) {
-                return $item[$key];
-            }
-        }
-    }
-
-    /**
-     * Return the key of the current element.
-     *
-     * @return string
-     */
-    #[\ReturnTypeWillChange]
-    public function key()
-    {
-        if (($this->endItemIdx !== null) && isset($this->lastItems[$this->endItemIdx])) {
-            return $this->lastItems[$this->endItemIdx][0];
-        } else {
-            if (isset($this->firstItems[$this->firstItemIdx])) {
-                return $this->firstItems[$this->firstItemIdx][0];
-            } else {
-                return $this->extractValue($this->items->current(), $this->keyField);
-            }
-        }
-    }
-
-    /**
-     * Move forward to next element.
-     *
-     * @return mixed
-     */
-    #[\ReturnTypeWillChange]
-    public function next()
-    {
-        $this->firstItemIdx++;
-
-        if (isset($this->firstItems[$this->firstItemIdx])) {
-            return $this->firstItems[$this->firstItemIdx][1];
-        } else {
-            if (!isset($this->firstItems[$this->firstItemIdx - 1])) {
-                $this->items->next();
-            }
-
-            if ($this->excludedItems) {
-                while (($c = $this->items->current()) && in_array($c->{$this->keyField}, $this->excludedItems ?? [], true)) {
-                    $this->items->next();
-                }
-            }
-        }
-
-        if (!$this->items->valid()) {
-            // iterator has passed the preface items, off the end of the items
-            // list. Track through the end items to go through to the next
-            if ($this->endItemIdx === null) {
-                $this->endItemIdx = -1;
-            }
-
-            $this->endItemIdx++;
-
-            if (isset($this->lastItems[$this->endItemIdx])) {
-                return $this->lastItems[$this->endItemIdx];
-            }
-
-            return false;
-        }
-    }
-
-    /**
-     * Checks if current position is valid.
-     *
-     * @return boolean
-     */
-    #[\ReturnTypeWillChange]
-    public function valid()
-    {
-        return (
-            (isset($this->firstItems[$this->firstItemIdx])) ||
-            (($this->endItemIdx !== null) && isset($this->lastItems[$this->endItemIdx])) ||
-            $this->items->valid()
-        );
-    }
-}