diff --git a/forms/FieldSet.php b/forms/FieldSet.php
index 227e20949..e09c6e6c7 100755
--- a/forms/FieldSet.php
+++ b/forms/FieldSet.php
@@ -471,26 +471,8 @@ class FieldSet extends DataObjectSet {
 	 * @param string|FormField
 	 */
 	function makeFieldReadonly($field) {
-		$fieldName = ($field instanceof FormField) ? $field->Name() : $field;
-		
-		// Iterate on items, looking for the applicable field
-		foreach($this->items as $i => $item) {
-			if($item->isComposite()) {
-				$item->makeFieldReadonly($fieldName);
-			} else {
-				// Once it's found, use FormField::transform to turn the field into a readonly version of itself.
-				if($item->Name() == $fieldName) {
-					$this->items[$i] = $item->transform(new ReadonlyTransformation());
-
-					// Clear an internal cache
-					$this->sequentialSet = null;
-
-					// A true results indicates that the field was foudn
-					return true;
-				}
-			}
-		}
-		return false;
+		$srcField = $this->dataFieldByName($fieldName);
+		$this->replaceField($fieldName, $srcField->performReadonlyTransformation());
 	}
 	
 	/**
@@ -552,4 +534,4 @@ class FieldSet extends DataObjectSet {
 	
 }
 
-?>
\ No newline at end of file
+?>