diff --git a/lib/MonetDBData.rb b/lib/MonetDBData.rb
index 4aaef8cc67824b5f96f8bb2f40c3644aef49e4da..3b06901db2123abc92d210974c51e3c4fe970b52 100644
--- a/lib/MonetDBData.rb
+++ b/lib/MonetDBData.rb
@@ -294,7 +294,7 @@ class MonetDBData
   def parse_tuple(tuple)
     fields = Array.new
     # remove trailing  "["
-    tuple = tuple.gsub(/^\[\s+/,'')
+    tuple = tuple.to_s.gsub(/^\[\s+/,'')
     
     tuple.split(/,\t/).each do |f|
       fields << f.gsub(/\\/, '').gsub(/^"/,'').gsub(/"$/,'').gsub(/\"/, '')