diff --git a/convert.scm b/convert.scm
index 3e905b5..cb38385 100644
--- a/convert.scm
+++ b/convert.scm
@@ -5,7 +5,9 @@
 (require-library srfi-4)
 
 (define (blob->seconds blob)
-  (u32vector-ref (blob->u32vector blob) 0))
+  (if (u32vector? blob)
+      (u32vector-ref (blob->u32vector blob) 0)
+      0))
 
 (define (convert-table db name converter #!optional select)
   (let ((count (first-result db (string-append "SELECT COUNT(*) FROM " name)))