diff --git a/include/mruby/internal.h b/include/mruby/internal.h
index 5215d0e51..17e867d7b 100644
--- a/include/mruby/internal.h
+++ b/include/mruby/internal.h
@@ -95,6 +95,7 @@ mrb_value mrb_rational_add(mrb_state *mrb, mrb_value x, mrb_value y);
 mrb_value mrb_rational_sub(mrb_state *mrb, mrb_value x, mrb_value y);
 mrb_value mrb_rational_mul(mrb_state *mrb, mrb_value x, mrb_value y);
 mrb_value mrb_rational_div(mrb_state *mrb, mrb_value x, mrb_value y);
+void mrb_rational_copy(mrb_state *mrb, mrb_value x, mrb_value y);
 #endif
 
 #ifdef MRUBY_PROC_H
diff --git a/mrbgems/mruby-bin-mrbc/tools/mrbc/stub.c b/mrbgems/mruby-bin-mrbc/tools/mrbc/stub.c
index 1ad628664..1513471c1 100644
--- a/mrbgems/mruby-bin-mrbc/tools/mrbc/stub.c
+++ b/mrbgems/mruby-bin-mrbc/tools/mrbc/stub.c
@@ -65,4 +65,7 @@ mrb_value mrb_rational_to_f(mrb_state *mrb, mrb_value x)
 {
   return mrb_nil_value();
 }
+void mrb_rational_copy(mrb_state *mrb, mrb_value x, mrb_value y)
+{
+}
 #endif
diff --git a/mrbgems/mruby-rational/src/rational.c b/mrbgems/mruby-rational/src/rational.c
index 70b8cc451..511e002e8 100644
--- a/mrbgems/mruby-rational/src/rational.c
+++ b/mrbgems/mruby-rational/src/rational.c
@@ -110,6 +110,15 @@ mrb_rational_new(mrb_state *mrb, mrb_int numerator, mrb_int denominator)
 
 #define rational_new(mrb,n,d) mrb_rational_new(mrb, n, d)
 
+void
+mrb_rational_copy(mrb_state *mrb, mrb_value x, mrb_value y)
+{
+  struct mrb_rational *p1 = rational_ptr(mrb, x);
+  struct mrb_rational *p2 = rational_ptr(mrb, y);
+  p1->numerator = p2->numerator;
+  p1->denominator = p2->denominator;
+}
+
 inline static mrb_int
 i_gcd(mrb_int x, mrb_int y)
 {
diff --git a/src/class.c b/src/class.c
index b8a2268c2..581a1a859 100644
--- a/src/class.c
+++ b/src/class.c
@@ -2742,6 +2742,11 @@ init_copy(mrb_state *mrb, mrb_value dest, mrb_value obj)
       mrb_bint_copy(mrb, dest, obj);
       break;
 #endif
+#ifdef MRB_USE_RATIONAL
+    case MRB_TT_RATIONAL:
+      mrb_rational_copy(mrb, dest, obj);
+      break;
+#endif
 
     default:
       break;