diff --git a/libcxx/include/__locale b/libcxx/include/__locale
--- a/libcxx/include/__locale
+++ b/libcxx/include/__locale
@@ -926,6 +926,14 @@
     return std::use_facet<ctype<_CharT> >(__loc).is(ctype_base::graph, __c);
 }
 
+template <class _CharT>
+_LIBCPP_HIDE_FROM_ABI
+bool
+isblank(_CharT __c, const locale& __loc)
+{
+    return std::use_facet<ctype<_CharT> >(__loc).is(ctype_base::blank, __c);
+}
+
 template <class _CharT>
 inline _LIBCPP_INLINE_VISIBILITY
 _CharT
diff --git a/libcxx/test/std/localization/locales/locale.convenience/classification/isblank.pass.cpp b/libcxx/test/std/localization/locales/locale.convenience/classification/isblank.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/localization/locales/locale.convenience/classification/isblank.pass.cpp
@@ -0,0 +1,33 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// <locale>
+
+// template <class charT> bool isblank (charT c, const locale& loc);
+
+#include <locale>
+#include <cassert>
+
+#include "test_macros.h"
+
+int main(int, char**) {
+  std::locale l;
+  assert(std::isblank(' ', l));
+  assert(!std::isblank('<', l));
+  assert(!std::isblank('\x8', l));
+  assert(!std::isblank('A', l));
+  assert(!std::isblank('a', l));
+  assert(!std::isblank('z', l));
+  assert(!std::isblank('3', l));
+  assert(!std::isblank('.', l));
+  assert(!std::isblank('f', l));
+  assert(!std::isblank('9', l));
+  assert(!std::isblank('+', l));
+
+  return 0;
+}