diff --git a/mrbgems/mruby-math/src/math.c b/mrbgems/mruby-math/src/math.c
index 02c63ce22..bf5ee9b5b 100644
--- a/mrbgems/mruby-math/src/math.c
+++ b/mrbgems/mruby-math/src/math.c
@@ -478,9 +478,8 @@ static mrb_value
 math_log(mrb_state *mrb, mrb_value obj)
 {
   mrb_float x, base;
-  mrb_int argc;
+  mrb_int argc = mrb_get_args(mrb, "f|f", &x, &base);
 
-  argc = mrb_get_args(mrb, "f|f", &x, &base);
   if (x < 0.0) {
     domain_error(mrb, "log");
   }