diff --git a/libstdc++-v3/testsuite/28_regex/basic_regex/assign/wchar_t/pstring.cc b/libstdc++-v3/testsuite/28_regex/basic_regex/assign/wchar_t/pstring.cc
index 2e9dea13a774..91e55129908c 100644
--- a/libstdc++-v3/testsuite/28_regex/basic_regex/assign/wchar_t/pstring.cc
+++ b/libstdc++-v3/testsuite/28_regex/basic_regex/assign/wchar_t/pstring.cc
@@ -23,6 +23,7 @@
 // [28.8.3] class template basic_regex assign()
 
 #include <regex>
+#include <cwchar>
 
 // Tests assign operation from a Pascal-style counted-string.  
 void test01()
@@ -31,7 +32,7 @@ void test01()
 
   const wchar_t cs[] = L"aab";
   test_type re;
-  re.assign(cs, sizeof(cs)-1, std::regex_constants::basic);
+  re.assign(cs, std::wcslen(cs), std::regex_constants::basic);
 }
 
 int