diff --git a/src/MimeDb.php b/src/MimeDb.php
index 03e47d5..f146a6a 100644
--- a/src/MimeDb.php
+++ b/src/MimeDb.php
@@ -120,7 +120,7 @@ public function findAllMimeTypesByExtension(string $lookupFileExtension): ?array
         $foundDbEntries = array_filter(
             $this->mimeDatabase,
             function ($mimetypeDefinition) use ($lookupFileExtension) {
-                return in_array(ltrim($lookupFileExtension, "."), $mimetypeDefinition['extensions']);
+                return in_array(strtolower(ltrim($lookupFileExtension, ".")), $mimetypeDefinition['extensions']);
             }
         );