diff --git a/lib/active_force/mapping.rb b/lib/active_force/mapping.rb
index <HASH>..<HASH> 100644
--- a/lib/active_force/mapping.rb
+++ b/lib/active_force/mapping.rb
@@ -61,7 +61,7 @@ module ActiveForce
       when *STRINGLIKE_TYPES
         value.to_s
       when :boolean
-        !['false','0','f'].include? value.downcase
+        !['false','0','f'].include? value.to_s.downcase
       when :int
         value.to_i
       when :double, :percent
Fix: set boolean to string before check on typecast_value.