diff --git a/ext/fiddle/pointer.c b/ext/fiddle/pointer.c
index 26119883..9f3813a2 100644
--- a/ext/fiddle/pointer.c
+++ b/ext/fiddle/pointer.c
@@ -813,7 +813,7 @@ rb_fiddle_ptr_read_mem(int argc, VALUE argv[], VALUE klass)
 {
     VALUE val, arg1;
 
-    switch (rb_scan_args(argc, argv, "11", &val, &arg1)) {
+    switch (rb_scan_args(argc, argv, "11", &val, &len)) {
       case 1:
           return rb_fiddle_ptr_s_to_ptr(klass, val);
 	break;