diff --git a/libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.static/hardware_concurrency.pass.cpp b/libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.static/hardware_concurrency.pass.cpp
--- a/libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.static/hardware_concurrency.pass.cpp
+++ b/libcxx/test/std/thread/thread.threads/thread.thread.class/thread.thread.static/hardware_concurrency.pass.cpp
@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads
-// XFAIL: LIBCXX-AIX-FIXME
 
 // <thread>
 
diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -115,8 +115,7 @@
 
 function generate-cmake-aix() {
     generate-cmake-base \
-          -S "${MONOREPO_ROOT}/llvm" \
-          -DLLVM_ENABLE_PROJECTS="libcxx;libcxxabi" \
+          -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
           "${@}"
 }
 
diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@@ -519,6 +519,12 @@
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${LIBCXXABI_CXX_FLAGS}")
 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${LIBCXXABI_C_FLAGS}")
 
+# On AIX, avoid picking up VMX extensions(i.e. vec_malloc) which would change
+# the default alignment of the allocators here.
+if (UNIX AND ${CMAKE_SYSTEM_NAME} MATCHES "AIX")
+  add_definitions("-D_XOPEN_SOURCE=700")
+endif()
+
 #===============================================================================
 # Setup Source Code
 #===============================================================================