diff --git a/test/ruby/enc/test_case_options.rb b/test/ruby/enc/test_case_options.rb
index 40a85ee970..e9c81d804e 100644
--- a/test/ruby/enc/test_case_options.rb
+++ b/test/ruby/enc/test_case_options.rb
@@ -19,7 +19,7 @@ class TestCaseOptions < Test::Unit::TestCase
 
   def assert_raise_both_types(*options)
     assert_raise_functional_operations 'a', *options
-    assert_raise_bang_operations +'a', *options
+    assert_raise_bang_operations(+'a', *options)
     assert_raise_functional_operations :a, *options
   end
 
@@ -51,7 +51,7 @@ class TestCaseOptions < Test::Unit::TestCase
 
   def assert_okay_both_types(*options)
     assert_okay_functional_operations 'a', *options
-    assert_okay_bang_operations +'a', *options
+    assert_okay_bang_operations(+'a', *options)
     assert_okay_functional_operations :a, *options
   end
 
diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index 0dae1c5a8e..9ff3791e7d 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -3620,11 +3620,11 @@ CODE
     assert_predicate chilled_string.clone, :frozen?
 
     # @+ treat the original string as frozen
-    assert_not_predicate +chilled_string, :frozen?
+    assert_not_predicate(+chilled_string, :frozen?)
     assert_not_same chilled_string, +chilled_string
 
     # @- the original string as mutable
-    assert_predicate -chilled_string, :frozen?
+    assert_predicate(-chilled_string, :frozen?)
     assert_not_same chilled_string, -chilled_string
   end