diff --git a/test/fiddle/helper.rb b/test/fiddle/helper.rb
index bc98f858ba..e98eecc198 100644
--- a/test/fiddle/helper.rb
+++ b/test/fiddle/helper.rb
@@ -26,7 +26,8 @@ when /linux/
   libm_so = File.join(libdir, "libm.so.6")
 when /mingw/, /mswin/
   require "rbconfig"
-  libc_so = libm_so = RbConfig::CONFIG["RUBY_SO_NAME"].split(/-/).find{|e| /^msvc/ =~ e} + ".dll"
+  crtname = RbConfig::CONFIG["RUBY_SO_NAME"][/^msvc\w+/] || 'ucrtbase'
+  libc_so = libm_so = "#{crtname}.dll"
 when /darwin/
   libc_so = "/usr/lib/libc.dylib"
   libm_so = "/usr/lib/libm.dylib"