diff --git a/mrbgems/mruby-random/src/random.c b/mrbgems/mruby-random/src/random.c
index db9483a55..fadd77abb 100644
--- a/mrbgems/mruby-random/src/random.c
+++ b/mrbgems/mruby-random/src/random.c
@@ -170,7 +170,7 @@ static mrb_value
 rand_range_float(mrb_state *mrb, rand_state *t,
                  mrb_float begin, mrb_float end,
                  mrb_bool excl) {
-  mrb_float span = end - begin + (excl ? 0.0 : 1.0);
+  mrb_float span = end - begin;
   if (span <= 0.0)
     return mrb_nil_value();