diff --git a/src/parser/ArcanistBundle.php b/src/parser/ArcanistBundle.php
--- a/src/parser/ArcanistBundle.php
+++ b/src/parser/ArcanistBundle.php
@@ -762,7 +762,7 @@
       $old_data = $this->getBlob($old_phid, $name);
     }
 
-    $old_length = strlen($old_data);
+    $old_length = phutil_nonempty_string($old_data) ? strlen($old_data) : 0;
 
     // Here, and below, the binary will be emitted with base85 encoding. This
     // encoding encodes each 4 bytes of input in 5 bytes of output, so we may
@@ -795,7 +795,7 @@
       $new_data = $this->getBlob($new_phid, $name);
     }
 
-    $new_length = strlen($new_data);
+    $new_length = phutil_nonempty_string($new_data) ? strlen($new_data) : 0;
     $this->reserveBytes($new_length * 5 / 4);
 
     if ($new_data === null) {