diff --git a/test/-ext-/string/test_modify_expand.rb b/test/-ext-/string/test_modify_expand.rb
index c7093e3892..b7f96426fc 100644
--- a/test/-ext-/string/test_modify_expand.rb
+++ b/test/-ext-/string/test_modify_expand.rb
@@ -16,6 +16,7 @@ class Test_StringModifyExpand < Test::Unit::TestCase
   end
 
   def test_integer_overflow
+    return if RbConfig::SIZEOF['size_t'] > RbConfig::SIZEOF['long']
     bug12390 = '[ruby-core:75592] [Bug #12390]'
     s = Bug::String.new
     long_max = (1 << (8 * RbConfig::SIZEOF['long'] - 1)) - 1