diff --git a/ext/transcode/main.php b/ext/transcode/main.php
index e284e81e..bc6abe30 100644
--- a/ext/transcode/main.php
+++ b/ext/transcode/main.php
@@ -167,6 +167,18 @@ class TranscodeImage extends Extension
     {
         global $config;
 
+        // this onDataUpload happens earlier (or could happen earlier) than handle_pixel.onDataUpload
+        // it mutates the image such that the incorrect mime type is not checked (checking against
+        // the post-transcode mime type instead). This is to  give user feedback on what the mime type
+        // was before potential transcoding (the original) at the time of upload, and that it failed if not allowed.
+        // does it break bulk image importing? ZIP? SVG? there are a few flows that are untested!
+        if ($config->get_bool(UploadConfig::MIME_CHECK_ENABLED) == true) {
+            $allowed_mimes = $config->get_array(UploadConfig::ALLOWED_MIME_STRINGS);
+            if (!MimeType::matches_array($event->mime, $allowed_mimes)) {
+                throw new UploadException("MIME type not supported: " . $event->mime);
+            }
+        }
+
         if ($config->get_bool(TranscodeConfig::UPLOAD) == true) {
             if ($event->mime === MimeType::GIF&&MimeType::is_animated_gif($event->tmpname)) {
                 return;
diff --git a/ext/upload/config.php b/ext/upload/config.php
index 8f4b5124..313b0536 100644
--- a/ext/upload/config.php
+++ b/ext/upload/config.php
@@ -11,4 +11,6 @@ class UploadConfig
     public const MIN_FREE_SPACE = "upload_min_free_space";
     public const TLSOURCE = "upload_tlsource";
     public const TRANSLOAD_ENGINE = "transload_engine";
+    public const MIME_CHECK_ENABLED = "mime_check_enabled";
+    public const ALLOWED_MIME_STRINGS = "allowed_mime_strings";
 }
diff --git a/ext/upload/main.php b/ext/upload/main.php
index 8ebc2f2d..d02a1f55 100644
--- a/ext/upload/main.php
+++ b/ext/upload/main.php
@@ -98,6 +98,12 @@ class Upload extends Extension
                 }
             }
         }
+
+        $config->set_default_bool(UploadConfig::MIME_CHECK_ENABLED, false);
+        $config->set_default_array(
+            UploadConfig::ALLOWED_MIME_STRINGS,
+            DataHandlerExtension::get_all_supported_mimes()
+        );
     }
 
     public function onSetupBuilding(SetupBuildingEvent $event)
@@ -119,8 +125,21 @@ class Upload extends Extension
         $sb->add_label("<i>PHP Limit = " . ini_get('upload_max_filesize') . "</i>");
         $sb->add_choice_option(UploadConfig::TRANSLOAD_ENGINE, $tes, "<br/>Transload: ");
         $sb->add_bool_option(UploadConfig::TLSOURCE, "<br/>Use transloaded URL as source if none is provided: ");
+
+        $sb->start_table();
+        $sb->add_bool_option(UploadConfig::MIME_CHECK_ENABLED, "Enable upload MIME checks", true);
+        $sb->add_multichoice_option(UploadConfig::ALLOWED_MIME_STRINGS, $this->get_mime_options(), "Allowed MIME uploads", true);
+        $sb->end_table();
     }
 
+    private function get_mime_options(): array
+    {
+        $output = [];
+        foreach (DataHandlerExtension::get_all_supported_mimes() as $mime) {
+            $output[MimeMap::get_name_for_mime($mime)] = $mime;
+        }
+        return $output;
+    }
 
     public function onPageNavBuilding(PageNavBuildingEvent $event)
     {