diff --git a/src/OutputFormatter.php b/src/OutputFormatter.php
index e7f2af64..c414e9e9 100644
--- a/src/OutputFormatter.php
+++ b/src/OutputFormatter.php
@@ -87,7 +87,7 @@ public function spaceAfterSelectorSeparator(): string
     }
 
     /**
-     * @param string $sSeparator
+     * @param non-empty-string $sSeparator
      */
     public function spaceBeforeListArgumentSeparator($sSeparator): string
     {
@@ -97,7 +97,7 @@ public function spaceBeforeListArgumentSeparator($sSeparator): string
     }
 
     /**
-     * @param string $sSeparator
+     * @param non-empty-string $sSeparator
      */
     public function spaceAfterListArgumentSeparator($sSeparator): string
     {