diff --git a/lib/rex/text.rb b/lib/rex/text.rb
index 755ca62d17..a7d12bd6ad 100644
--- a/lib/rex/text.rb
+++ b/lib/rex/text.rb
@@ -756,6 +756,8 @@ module Text
 		buf = ''
 		idx = 0
 		offsets = []
+		# Make sure there's something in sets even if we were given an explicit nil
+		sets ||= [ UpperAlpha, LowerAlpha, Numerals ]
 
 		sets.length.times { offsets << 0 }