diff --git a/src/applications/files/conduit/FileConduitAPIMethod.php b/src/applications/files/conduit/FileConduitAPIMethod.php
--- a/src/applications/files/conduit/FileConduitAPIMethod.php
+++ b/src/applications/files/conduit/FileConduitAPIMethod.php
@@ -81,6 +81,9 @@
   }
 
   protected function decodeBase64($data) {
+    if (!phutil_nonempty_string($data)) {
+      throw new Exception(pht('Empty base64 data!'));
+    }
     $data = base64_decode($data, $strict = true);
     if ($data === false) {
       throw new Exception(pht('Unable to decode base64 data!'));