diff --git a/libcxx/docs/ReleaseNotes.rst b/libcxx/docs/ReleaseNotes.rst
--- a/libcxx/docs/ReleaseNotes.rst
+++ b/libcxx/docs/ReleaseNotes.rst
@@ -78,6 +78,12 @@
   exceeds the maximum supported size, as required by the C++ standard.
   Previously the type ``std::length_error`` was used.
 
+ABI Changes
+-----------
+
+- The C++17 variable templates ``is_error_code_enum_v`` and
+  ``is_error_condition_enum_v`` are now of type ``bool`` instead of ``size_t``.
+
 Build System Changes
 --------------------
 
diff --git a/libcxx/include/system_error b/libcxx/include/system_error
--- a/libcxx/include/system_error
+++ b/libcxx/include/system_error
@@ -46,10 +46,10 @@
     : public false_type {};
 
 template <class _Tp>
-inline constexpr size_t is_error_condition_enum_v = is_error_condition_enum<_Tp>::value; // C++17
+inline constexpr bool is_error_condition_enum_v = is_error_condition_enum<_Tp>::value; // C++17
 
 template <class _Tp>
-inline constexpr size_t is_error_code_enum_v = is_error_code_enum<_Tp>::value; // C++17
+inline constexpr bool is_error_code_enum_v = is_error_code_enum<_Tp>::value; // C++17
 
 class error_code
 {
@@ -165,7 +165,7 @@
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
-inline constexpr size_t is_error_code_enum_v = is_error_code_enum<_Tp>::value;
+inline constexpr bool is_error_code_enum_v = is_error_code_enum<_Tp>::value;
 #endif
 
 // is_error_condition_enum
@@ -176,7 +176,7 @@
 
 #if _LIBCPP_STD_VER > 14
 template <class _Tp>
-inline constexpr size_t is_error_condition_enum_v = is_error_condition_enum<_Tp>::value;
+inline constexpr bool is_error_condition_enum_v = is_error_condition_enum<_Tp>::value;
 #endif
 
 template <>
diff --git a/libcxx/test/std/diagnostics/syserr/is_error_code_enum.pass.cpp b/libcxx/test/std/diagnostics/syserr/is_error_code_enum.pass.cpp
--- a/libcxx/test/std/diagnostics/syserr/is_error_code_enum.pass.cpp
+++ b/libcxx/test/std/diagnostics/syserr/is_error_code_enum.pass.cpp
@@ -23,6 +23,7 @@
     static_assert((std::is_error_code_enum<T>::value == Expected), "");
 #if TEST_STD_VER > 14
     static_assert((std::is_error_code_enum_v<T>      == Expected), "");
+    ASSERT_SAME_TYPE(decltype(std::is_error_code_enum_v<T>), const bool);
 #endif
 }
 
diff --git a/libcxx/test/std/diagnostics/syserr/is_error_condition_enum.pass.cpp b/libcxx/test/std/diagnostics/syserr/is_error_condition_enum.pass.cpp
--- a/libcxx/test/std/diagnostics/syserr/is_error_condition_enum.pass.cpp
+++ b/libcxx/test/std/diagnostics/syserr/is_error_condition_enum.pass.cpp
@@ -23,6 +23,7 @@
     static_assert((std::is_error_condition_enum<T>::value == Expected), "");
 #if TEST_STD_VER > 14
     static_assert((std::is_error_condition_enum_v<T>        == Expected), "");
+    ASSERT_SAME_TYPE(decltype(std::is_error_condition_enum_v<T>), const bool);
 #endif
 }