diff --git a/libcxx/include/__format/parser_std_format_spec.h b/libcxx/include/__format/parser_std_format_spec.h
--- a/libcxx/include/__format/parser_std_format_spec.h
+++ b/libcxx/include/__format/parser_std_format_spec.h
@@ -108,7 +108,7 @@
   };
 
   _Type __type{_Type::__default};
-};
+} __attribute__((packed));
 
 namespace __detail {
 template <class _CharT>
diff --git a/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_bool.pass.cpp b/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_bool.pass.cpp
--- a/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_bool.pass.cpp
+++ b/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_bool.pass.cpp
@@ -8,7 +8,6 @@
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 // UNSUPPORTED: libcpp-no-concepts
 // UNSUPPORTED: libcpp-has-no-incomplete-format
-// XFAIL: LIBCXX-AIX-FIXME
 
 // <format>
 
diff --git a/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_char.pass.cpp b/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_char.pass.cpp
--- a/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_char.pass.cpp
+++ b/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_char.pass.cpp
@@ -8,7 +8,6 @@
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 // UNSUPPORTED: libcpp-no-concepts
 // UNSUPPORTED: libcpp-has-no-incomplete-format
-// XFAIL: LIBCXX-AIX-FIXME
 
 // <format>
 
diff --git a/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_integer.pass.cpp b/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_integer.pass.cpp
--- a/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_integer.pass.cpp
+++ b/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_integer.pass.cpp
@@ -8,7 +8,6 @@
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 // UNSUPPORTED: libcpp-no-concepts
 // UNSUPPORTED: libcpp-has-no-incomplete-format
-// XFAIL: LIBCXX-AIX-FIXME
 
 // <format>
 
diff --git a/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_string.pass.cpp b/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_string.pass.cpp
--- a/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_string.pass.cpp
+++ b/libcxx/test/libcxx/utilities/format/format.string/format.string.std/std_format_spec_string.pass.cpp
@@ -8,7 +8,6 @@
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 // UNSUPPORTED: libcpp-no-concepts
 // UNSUPPORTED: libcpp-has-no-incomplete-format
-// XFAIL: LIBCXX-AIX-FIXME
 
 // <format>