diff --git a/libcxx/include/ios b/libcxx/include/ios
index 61d00b90ee04..0bffa571e92b 100644
--- a/libcxx/include/ios
+++ b/libcxx/include/ios
@@ -592,6 +592,9 @@ public:
     typedef typename traits_type::pos_type pos_type;
     typedef typename traits_type::off_type off_type;
 
+    static_assert((is_same<_CharT, typename traits_type::char_type>::value),
+                  "traits_type::char_type must be the same type as CharT");
+
   // __true_value will generate undefined references when linking unless
   // we give it internal linkage.
 
diff --git a/libcxx/include/streambuf b/libcxx/include/streambuf
index ea64f5780459..e409d2106070 100644
--- a/libcxx/include/streambuf
+++ b/libcxx/include/streambuf
@@ -132,6 +132,9 @@ public:
     typedef typename traits_type::pos_type pos_type;
     typedef typename traits_type::off_type off_type;
 
+    static_assert((is_same<_CharT, typename traits_type::char_type>::value),
+                  "traits_type::char_type must be the same type as CharT");
+
     virtual ~basic_streambuf();
 
     // 27.6.2.2.1 locales:
diff --git a/libcxx/test/libcxx/input.output/file.streams/fstreams/filebuf/traits_mismatch.fail.cpp b/libcxx/test/libcxx/input.output/file.streams/fstreams/filebuf/traits_mismatch.fail.cpp
new file mode 100644
index 000000000000..84045cf3c94f
--- /dev/null
+++ b/libcxx/test/libcxx/input.output/file.streams/fstreams/filebuf/traits_mismatch.fail.cpp
@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <fstream>
+
+// template<class charT, class traits = char_traits<charT>>
+//   class basic_filebuf;
+//
+// The char type of the stream and the char_type of the traits have to match
+
+#include <fstream>
+
+int main()
+{
+	std::basic_filebuf<char, std::char_traits<wchar_t> > f;
+//  expected-error-re@streambuf:* {{static_assert failed{{.*}} "traits_type::char_type must be the same type as CharT"}}
+}
+
diff --git a/libcxx/test/libcxx/input.output/file.streams/fstreams/traits_mismatch.fail.cpp b/libcxx/test/libcxx/input.output/file.streams/fstreams/traits_mismatch.fail.cpp
new file mode 100644
index 000000000000..dcb7b1f64480
--- /dev/null
+++ b/libcxx/test/libcxx/input.output/file.streams/fstreams/traits_mismatch.fail.cpp
@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <fstream>
+
+// template <class charT, class traits = char_traits<charT> >
+// class basic_fstream
+
+// The char type of the stream and the char_type of the traits have to match
+
+#include <fstream>
+
+int main()
+{
+	std::basic_fstream<char, std::char_traits<wchar_t> > f;
+//  expected-error-re@ios:* {{static_assert failed{{.*}} "traits_type::char_type must be the same type as CharT"}}
+//  expected-error-re@streambuf:* {{static_assert failed{{.*}} "traits_type::char_type must be the same type as CharT"}}
+}
+
diff --git a/libcxx/test/libcxx/input.output/iostream.format/input.streams/traits_mismatch.fail.cpp b/libcxx/test/libcxx/input.output/iostream.format/input.streams/traits_mismatch.fail.cpp
new file mode 100644
index 000000000000..a459ec4fb71b
--- /dev/null
+++ b/libcxx/test/libcxx/input.output/iostream.format/input.streams/traits_mismatch.fail.cpp
@@ -0,0 +1,29 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <istream>
+
+// template <class charT, class traits = char_traits<charT> >
+// class basic_istream;
+
+// The char type of the stream and the char_type of the traits have to match
+
+#include <istream>
+#include <type_traits>
+#include <cassert>
+
+struct test_istream
+    : public std::basic_istream<char, std::char_traits<wchar_t> > {};
+
+
+int main()
+{
+//  expected-error-re@ios:* {{static_assert failed{{.*}} "traits_type::char_type must be the same type as CharT"}}
+}
+
diff --git a/libcxx/test/libcxx/input.output/iostream.format/output.streams/traits_mismatch.fail.cpp b/libcxx/test/libcxx/input.output/iostream.format/output.streams/traits_mismatch.fail.cpp
new file mode 100644
index 000000000000..fab0dd436577
--- /dev/null
+++ b/libcxx/test/libcxx/input.output/iostream.format/output.streams/traits_mismatch.fail.cpp
@@ -0,0 +1,29 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <ostream>
+
+// template <class charT, class traits = char_traits<charT> >
+// class basic_ostream;
+
+// The char type of the stream and the char_type of the traits have to match
+
+#include <ostream>
+#include <type_traits>
+#include <cassert>
+
+struct test_ostream
+    : public std::basic_ostream<char, std::char_traits<wchar_t> > {};
+
+
+int main()
+{
+//  expected-error-re@ios:* {{static_assert failed{{.*}} "traits_type::char_type must be the same type as CharT"}}
+}
+
diff --git a/libcxx/test/libcxx/input.output/string.streams/traits_mismatch.fail.cpp b/libcxx/test/libcxx/input.output/string.streams/traits_mismatch.fail.cpp
new file mode 100644
index 000000000000..f048cae0c565
--- /dev/null
+++ b/libcxx/test/libcxx/input.output/string.streams/traits_mismatch.fail.cpp
@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <sstream>
+
+//  template<class charT, class traits = char_traits<charT>,
+//           class Allocator = allocator<charT>>
+//    class basic_stringbuf;
+//
+// The char type of the stream and the char_type of the traits have to match
+
+#include <sstream>
+
+int main()
+{
+	std::basic_stringbuf<char, std::char_traits<wchar_t> > sb;
+//  expected-error-re@streambuf:* {{static_assert failed{{.*}} "traits_type::char_type must be the same type as CharT"}}
+//  expected-error-re@string:* {{static_assert failed{{.*}} "traits_type::char_type must be the same type as CharT"}}
+}
+