diff --git a/model/UnsavedRelationList.php b/model/UnsavedRelationList.php
index 2a7ef640d..35aee6049 100644
--- a/model/UnsavedRelationList.php
+++ b/model/UnsavedRelationList.php
@@ -199,6 +199,26 @@ class UnsavedRelationList extends ArrayList {
 		$this->addMany($idList);
 	}
 
+	/**
+	 * Returns an array with both the keys and values set to the IDs of the records in this list.
+	 *
+	 * Does not return the IDs for unsaved DataObjects
+	 */
+	public function getIDList() {
+		// Get a list of IDs of our current items - if it's not a number then object then assume it's a DO.
+		$ids = array_map(function($obj) {
+			return is_numeric($obj) ? $obj : $obj->ID;
+		}, $this->items);
+
+		// Strip out duplicates and anything resolving to False.
+		$ids = array_filter(array_unique($ids));
+
+		// Change the array from (1, 2, 3) to (1 => 1, 2 => 2, 3 => 3)
+		if ($ids) $ids = array_combine($ids, $ids);
+
+		return $ids;
+	}
+
 	/**
 	 * Returns the first item in the list
 	 *
@@ -294,10 +314,6 @@ class UnsavedRelationList extends ArrayList {
 		throw new LogicException(__FUNCTION__ . " can't be called on an UnsavedRelationList.");
 	}
 
-	public function getIDList() {
-		throw new LogicException(__FUNCTION__ . " can't be called on an UnsavedRelationList.");
-	}
-
 	public function getRange($offset, $length) {
 		throw new LogicException(__FUNCTION__ . " can't be called on an UnsavedRelationList.");
 	}
diff --git a/tests/model/UnsavedRelationListTest.php b/tests/model/UnsavedRelationListTest.php
index 57f011eb6..c2968d85b 100644
--- a/tests/model/UnsavedRelationListTest.php
+++ b/tests/model/UnsavedRelationListTest.php
@@ -157,6 +157,32 @@ class UnsavedRelationListTest extends SapphireTest {
 			array('Name' => 'C', 'Number' => 3)
 		), $object->Siblings());
 	}
+
+	public function testGetIDList() {
+		$object = new UnsavedRelationListTest_DataObject;
+
+		$children = $object->Children();
+		$this->assertEquals($children->getIDList(), array());
+		$children->add($child1 = new UnsavedRelationListTest_DataObject(array('Name' => 'A')));
+		$children->add($child2 = new UnsavedRelationListTest_DataObject(array('Name' => 'B')));
+		$children->add($child3 = new UnsavedRelationListTest_DataObject(array('Name' => 'C')));
+		$children->add($child1);
+
+		$this->assertEquals($children->getIDList(), array());
+
+		$child1->write();
+		$this->assertEquals($children->getIDList(), array(
+			$child1->ID => $child1->ID
+		));
+
+		$child2->write();
+		$child3->write();
+		$this->assertEquals($children->getIDList(), array(
+			$child1->ID => $child1->ID,
+			$child2->ID => $child2->ID,
+			$child3->ID => $child3->ID
+		));
+	}
 }
 
 class UnsavedRelationListTest_DataObject extends DataObject implements TestOnly {