diff --git a/lib/includes/Formatters/ControlledFallbackEntityIdFormatter.php b/lib/includes/Formatters/ControlledFallbackEntityIdFormatter.php
index 52a41811f..1b200ea12 100644
--- a/lib/includes/Formatters/ControlledFallbackEntityIdFormatter.php
+++ b/lib/includes/Formatters/ControlledFallbackEntityIdFormatter.php
@@ -71,7 +71,13 @@ class ControlledFallbackEntityIdFormatter implements EntityIdFormatter {
        }

        public function formatEntityId( EntityId $value ) {
-               if ( $value instanceof Int32EntityId && $value->getNumericId() <= $this->maxEntityId ) {
+               $testHeader = \RequestContext::getMain()->getRequest()->getHeader( 'X-WIKIBASE-formatEntityId' );
+               wfDebugLog( 'AdHocDebug', json_encode( $testHeader ) );
+               if (
+                       ( $value instanceof Int32EntityId && $value->getNumericId() <= $this->maxEntityId && $testHeader !== 'old' ) ||
+                       ( $testHeader === 'new' )
+               ) {
+                       wfDebugLog( 'AdHocDebug', 'Trying new / target formatter' );
                        try {
                                $formatEntityId = $this->targetFormatter->formatEntityId( $value );
                                $this->statsdDataFactory->increment( $this->statsPrefix . 'targetFormatterCalled' );