diff --git a/libcxx/include/__config b/libcxx/include/__config
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -312,6 +312,14 @@
 #  define _LIBCPP_SHORT_WCHAR   1
 #endif
 
+#if defined(_AIX) || defined(__MVS__)
+// On AIX and zOS in 64-bit, wint_t is not able to represent any wchar_t value as well as WEOF
+// because wint_t and wchar_t have the same size, consequently an additional member is 
+// needed to indicate if the fill value is initialized.
+// Enabled in 32-bit for compatibility with the IBM AIX/zOS provided libc++.
+#  define _LIBCPP_BASIC_IOS_HAS_FILL_SET 1
+#endif
+
 // Libc++ supports various implementations of std::random_device.
 //
 // _LIBCPP_USING_DEV_RANDOM
diff --git a/libcxx/include/ios b/libcxx/include/ios
--- a/libcxx/include/ios
+++ b/libcxx/include/ios
@@ -680,6 +680,9 @@
 private:
     basic_ostream<char_type, traits_type>* __tie_;
     mutable int_type __fill_;
+#if defined(_LIBCPP_BASIC_IOS_HAS_FILL_SET)
+    bool __fill_set_;
+#endif
 };
 
 template <class _CharT, class _Traits>
@@ -702,6 +705,9 @@
     ios_base::init(__sb);
     __tie_ = nullptr;
     __fill_ = traits_type::eof();
+#if defined(_LIBCPP_BASIC_IOS_HAS_FILL_SET)
+    __fill_set_ = false;
+#endif
 }
 
 template <class _CharT, class _Traits>
@@ -773,7 +779,11 @@
 _CharT
 basic_ios<_CharT, _Traits>::fill() const
 {
+#if defined(_LIBCPP_BASIC_IOS_HAS_FILL_SET)
+    if (!__fill_set_)
+#else
     if (traits_type::eq_int_type(traits_type::eof(), __fill_))
+#endif
         __fill_ = widen(' ');
     return __fill_;
 }
@@ -783,10 +793,17 @@
 _CharT
 basic_ios<_CharT, _Traits>::fill(char_type __ch)
 {
+#if defined(_LIBCPP_BASIC_IOS_HAS_FILL_SET)
+    if (!__fill_set_)
+#else
     if (traits_type::eq_int_type(traits_type::eof(), __fill_))
+#endif
         __fill_ = widen(' ');
     char_type __r = __fill_;
     __fill_ = __ch;
+#if defined(_LIBCPP_BASIC_IOS_HAS_FILL_SET)
+    __fill_set_ = true;
+#endif    
     return __r;
 }
 
@@ -800,6 +817,9 @@
         ios_base::copyfmt(__rhs);
         __tie_ = __rhs.__tie_;
         __fill_ = __rhs.__fill_;
+#if defined(_LIBCPP_BASIC_IOS_HAS_FILL_SET)
+        __fill_set_ = __rhs.__fill_set_;
+#endif
         __call_callbacks(copyfmt_event);
         exceptions(__rhs.exceptions());
     }
@@ -815,6 +835,9 @@
     __tie_ = __rhs.__tie_;
     __rhs.__tie_ = nullptr;
     __fill_ = __rhs.__fill_;
+#if defined(_LIBCPP_BASIC_IOS_HAS_FILL_SET)
+    __fill_set_ = __rhs.__fill_set_;
+#endif
 }
 
 template <class _CharT, class _Traits>
@@ -825,6 +848,9 @@
     ios_base::swap(__rhs);
     _VSTD::swap(__tie_, __rhs.__tie_);
     _VSTD::swap(__fill_, __rhs.__fill_);
+#if defined(_LIBCPP_BASIC_IOS_HAS_FILL_SET)
+    _VSTD::swap(__fill_set_, __rhs.__fill_set_);
+#endif
 }
 
 template <class _CharT, class _Traits>
diff --git a/libcxx/test/std/input.output/iostream.format/std.manip/setfill.pass.cpp b/libcxx/test/std/input.output/iostream.format/std.manip/setfill.pass.cpp
--- a/libcxx/test/std/input.output/iostream.format/std.manip/setfill.pass.cpp
+++ b/libcxx/test/std/input.output/iostream.format/std.manip/setfill.pass.cpp
@@ -13,6 +13,7 @@
 #include <iomanip>
 #include <ostream>
 #include <cassert>
+#include <limits>
 
 #include "test_macros.h"
 
@@ -38,6 +39,13 @@
         os << std::setfill(L'*');
         assert(os.fill() == L'*');
     }
+
+    {
+        testbuf<wchar_t> sb;
+        std::wostream os(&sb);
+        os << std::setfill(std::numeric_limits<wchar_t>::max());
+        assert(os.fill() == std::numeric_limits<wchar_t>::max());
+    }
 #endif
 
   return 0;