diff --git a/src/Form/PatternDisplayFormTrait.php b/src/Form/PatternDisplayFormTrait.php
index 1480332d4ec37889dca01f0091a6cf8c73e21bc3..ce39eb8bdd0e284d215a7ee475472be067fcc81f 100644
--- a/src/Form/PatternDisplayFormTrait.php
+++ b/src/Form/PatternDisplayFormTrait.php
@@ -144,7 +144,7 @@ trait PatternDisplayFormTrait {
           unset($settings['pattern_mapping'][$key]);
         }
         else {
-          list($plugin, $source) = explode(PatternSourceBase::DERIVATIVE_SEPARATOR, $key);
+          list($plugin, $source) = explode(PatternSourceBase::DERIVATIVE_SEPARATOR, $key, 2);
           $settings['pattern_mapping'][$key]['plugin'] = $plugin;
           $settings['pattern_mapping'][$key]['source'] = $source;
         }