Index: ext/dl/callback/mkcallback.rb
===================================================================
--- ext/dl/callback/mkcallback.rb	(revision 22794)
+++ ext/dl/callback/mkcallback.rb	(working copy)
@@ -71,7 +71,7 @@
   FLOAT => {
     :name => 'float',
     :type => 'float',
-    :conv => 'RFLOAT_VALUE(%s)',
+    :conv => '(float)RFLOAT_VALUE(%s)',
   },
   DOUBLE => {
     :name => 'double',