diff --git a/bootstraptest/test_ractor.rb b/bootstraptest/test_ractor.rb
index b1e9e3a79d..a13c5237af 100644
--- a/bootstraptest/test_ractor.rb
+++ b/bootstraptest/test_ractor.rb
@@ -434,8 +434,8 @@ assert_equal "allocator undefined for Thread", %q{
     r = Ractor.new obj do |msg|
       msg
     end
-  rescue TypeError => e
-    e.message #=> no _dump_data is defined for class Thread
+  rescue Ractor::IsolationError => e
+    e.cause.message #=> no _dump_data is defined for class Thread
   else
     'ng'
   end
@@ -1429,7 +1429,7 @@ assert_equal "ok", %q{
   end
   begin
     Ractor.new{} << err
-  rescue TypeError
+  rescue Ractor::IsolationError
     'ok'
   end
 }
diff --git a/ractor.c b/ractor.c
index 096bda5df6..f66c25c486 100644
--- a/ractor.c
+++ b/ractor.c
@@ -1945,7 +1945,12 @@ copy_enter(VALUE obj, struct obj_traverse_replace_data *data)
         return traverse_skip;
     }
     else {
-        data->replacement = rb_obj_clone(obj);
+        int state;
+        VALUE result = rb_protect(rb_obj_clone, obj, &state);
+        if (state) {
+            rb_raise(rb_eRactorIsolationError, "cannot copy %"PRIsVALUE"", obj);
+        }
+        data->replacement = result;
         return traverse_cont;
     }
 }
diff --git a/test/ruby/test_ractor.rb b/test/ruby/test_ractor.rb
index 74de2bf9cd..7e4e51ac34 100644
--- a/test/ruby/test_ractor.rb
+++ b/test/ruby/test_ractor.rb
@@ -30,6 +30,10 @@ class TestRactor < Test::Unit::TestCase
     assert_make_shareable(x)
   end
 
+  def test_cannot_copy_proc
+    assert_unshareable(-> { }, /cannot copy/, copy: true)
+  end
+
   def test_shareability_of_method_proc
     str = +""
 
@@ -207,10 +211,10 @@ class TestRactor < Test::Unit::TestCase
     assert Ractor.shareable?(obj), "object didn't become shareable"
   end
 
-  def assert_unshareable(obj, msg=nil, exception: Ractor::IsolationError)
+  def assert_unshareable(obj, msg=nil, copy: false, exception: Ractor::IsolationError)
     refute Ractor.shareable?(obj), "object is already shareable"
     assert_raise_with_message(exception, msg) do
-      Ractor.make_shareable(obj)
+      Ractor.make_shareable(obj, copy:)
     end
     refute Ractor.shareable?(obj), "despite raising, object became shareable"
   end