diff --git a/lib/liquid/expression.rb b/lib/liquid/expression.rb
index b5178d38..9a48952a 100644
--- a/lib/liquid/expression.rb
+++ b/lib/liquid/expression.rb
@@ -79,6 +79,10 @@ module Liquid
       end
 
       def parse_number(markup, ss)
+        # Quick reject: first byte must be digit or dash
+        first = markup.getbyte(0)
+        return false if first != DASH && (first < ZERO || first > NINE)
+
         # check if the markup is simple integer or float
         case markup
         when INTEGER_REGEX