diff --git a/core/modules/file/file.module b/core/modules/file/file.module
index 20e3d4e68e..eb325df072 100644
--- a/core/modules/file/file.module
+++ b/core/modules/file/file.module
@@ -1012,11 +1012,6 @@ function _file_save_upload_single(\SplFileInfo $file_info, $form_field_name, $va
         }
         $file->setFilename(file_munge_filename($filename, $extensions));
         \Drupal::messenger()->addStatus(t('For security reasons, your upload has been renamed to %filename.', ['%filename' => $file->getFilename()]));
-        // The .txt extension may not be in the allowed list of extensions. We
-        // have to add it here or else the file upload will fail.
-        if (!empty($validators['file_validate_extensions'][0])) {
-          $validators['file_validate_extensions'][0] .= ' txt';
-        }
       }
     }
   }
diff --git a/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php b/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
index 17fee8558f..d709552883 100644
--- a/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
+++ b/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
@@ -485,7 +485,6 @@ protected function prepareFilename($filename, array &$validators) {
         // If the file will be rejected anyway due to a disallowed extension, it
         // should not be renamed; rather, we'll let file_validate_extensions()
         // reject it below.
-        $passes_validation = FALSE;
         if (!empty($validators['file_validate_extensions'][0])) {
           $file = File::create([]);
           $file->setFilename($filename);
@@ -493,18 +492,17 @@ protected function prepareFilename($filename, array &$validators) {
           // Only allow upload and rename to .txt if .txt files are allowed.
           $passes_validation = $passes_validation && preg_match('/(^|\s)txt(\s|$)/', $validators['file_validate_extensions'][0]);
         }
-        if (empty($validators['file_validate_extensions'][0]) || $passes_validation) {
+        else {
+          // All file extensions are allowed.
+          $passes_validation = TRUE;
+        }
+
+        if ($passes_validation) {
           if ((substr($filename, -4) != '.txt')) {
             // The destination filename will also later be used to create the URI.
             $filename .= '.txt';
           }
           $filename = file_munge_filename($filename, $validators['file_validate_extensions'][0] ?? '');
-
-          // The .txt extension may not be in the allowed list of extensions. We
-          // have to add it here or else the file upload will fail.
-          if (!empty($validators['file_validate_extensions'][0])) {
-            $validators['file_validate_extensions'][0] .= ' txt';
-          }
         }
       }
     }
diff --git a/core/modules/jsonapi/src/Controller/TemporaryJsonapiFileFieldUploader.php b/core/modules/jsonapi/src/Controller/TemporaryJsonapiFileFieldUploader.php
index 5c046b1982..d49cad8e42 100644
--- a/core/modules/jsonapi/src/Controller/TemporaryJsonapiFileFieldUploader.php
+++ b/core/modules/jsonapi/src/Controller/TemporaryJsonapiFileFieldUploader.php
@@ -403,7 +403,6 @@ protected function prepareFilename($filename, array &$validators) {
         // If the file will be rejected anyway due to a disallowed extension, it
         // should not be renamed; rather, we'll let file_validate_extensions()
         // reject it below.
-        $passes_validation = FALSE;
         if (!empty($validators['file_validate_extensions'][0])) {
           $file = File::create([]);
           $file->setFilename($filename);
@@ -411,18 +410,17 @@ protected function prepareFilename($filename, array &$validators) {
           // Only allow upload and rename to .txt if .txt files are allowed.
           $passes_validation = $passes_validation && preg_match('/(^|\s)txt(\s|$)/', $validators['file_validate_extensions'][0]);
         }
-        if (empty($validators['file_validate_extensions'][0]) || $passes_validation) {
+        else {
+          // All file extensions are allowed.
+          $passes_validation = TRUE;
+        }
+
+        if ($passes_validation) {
           if (substr($filename, -4) != '.txt') {
             // The destination filename will also later be used to create the URI.
             $filename .= '.txt';
           }
           $filename = file_munge_filename($filename, $validators['file_validate_extensions'][0] ?? '');
-
-          // The .txt extension may not be in the allowed list of extensions. We
-          // have to add it here or else the file upload will fail.
-          if (!empty($validators['file_validate_extensions'][0])) {
-            $validators['file_validate_extensions'][0] .= ' txt';
-          }
         }
       }
     }