diff --git a/buildbot/osuosl/master/config/builders.py b/buildbot/osuosl/master/config/builders.py
--- a/buildbot/osuosl/master/config/builders.py
+++ b/buildbot/osuosl/master/config/builders.py
@@ -1,6 +1,7 @@
 from buildbot.process.properties import WithProperties
 
 from zorg.buildbot.builders import ClangBuilder
+from zorg.buildbot.builders import FlangBuilder
 from zorg.buildbot.builders import PollyBuilder
 from zorg.buildbot.builders import LLDBBuilder
 from zorg.buildbot.builders import SanitizerBuilder
@@ -1553,6 +1554,24 @@
          ),
          'category' : 'flang'},
 
+        {'name': "flang-aarch64-ubuntu-out-of-tree",
+         'slavenames':["linaro-aarch64-flang-oot"],
+         'builddir':"flang-aarch64-out-of-tree",
+         'factory': FlangBuilder.getFlangOutOfTreeBuildFactory(
+             llvm_extra_configure_args=[
+                 "-DLLVM_TARGETS_TO_BUILD=AArch64",
+                 "-DCMAKE_CXX_STANDARD=17",
+                 "-DLLVM_ENABLE_WERROR=OFF",
+                 "-DLLVM_ENABLE_ASSERTIONS=ON",
+                 "-DCMAKE_BUILD_TYPE=Release",
+             ],
+             flang_extra_configure_args=[
+                 "-DFLANG_ENABLE_WERROR=ON",
+                 "-DCMAKE_BUILD_TYPE=Release",
+            ],
+        ),
+        'category' : 'flang'},
+
         {'name': "flang-x86_64-linux",
          'slavenames':["nersc-flang"],
          'builddir':"flang-x86_64-linux",
diff --git a/buildbot/osuosl/master/config/slaves.py b/buildbot/osuosl/master/config/slaves.py
--- a/buildbot/osuosl/master/config/slaves.py
+++ b/buildbot/osuosl/master/config/slaves.py
@@ -44,6 +44,7 @@
         create_slave("linaro-aarch64-full", properties={'jobs' : 32}, max_builds=1),
         create_slave("linaro-aarch64-global-isel", properties={'jobs' : 32}, max_builds=1),
         create_slave("linaro-aarch64-lld", properties={'jobs' : 32}, max_builds=1),
+        create_slave("linaro-aarch64-flang-oot", properties={'jobs' : 32}, max_builds=1),
         # Libcxx testsuite has tests with timing assumptions.  Run single-threaded to make
         # sure we have plenty CPU cycle to satisfy timing assumptions.
         create_slave("linaro-aarch64-libcxx", properties={'jobs' : 1}, max_builds=1),
diff --git a/zorg/buildbot/builders/FlangBuilder.py b/zorg/buildbot/builders/FlangBuilder.py
new file mode 100644
--- /dev/null
+++ b/zorg/buildbot/builders/FlangBuilder.py
@@ -0,0 +1,72 @@
+from zorg.buildbot.commands.CmakeCommand import CmakeCommand
+
+from zorg.buildbot.process.factory import LLVMBuildFactory
+
+from zorg.buildbot.builders.UnifiedTreeBuilder import addNinjaSteps, getCmakeWithNinjaBuildFactory
+
+def getFlangOutOfTreeBuildFactory(
+           checks = None,
+           clean = False,
+           llvm_extra_configure_args = None,
+           flang_extra_configure_args = None,
+           env = None,
+           **kwargs):
+
+    f = getCmakeWithNinjaBuildFactory(
+            depends_on_projects=['llvm','mlir'],
+            obj_dir="build_llvm",
+            checks=[],
+            clean=clean,
+            extra_configure_args=llvm_extra_configure_args,
+            env=env,
+            **kwargs)
+
+    if checks is None:
+        checks = ['check-all']
+
+    # Make a local copy of the flang configure args, as we are going to modify that.
+    if flang_extra_configure_args:
+        flang_cmake_args = flang_extra_configure_args[:]
+    else:
+        flang_cmake_args = list()
+
+    # Some options are required for this build no matter what.
+    CmakeCommand.applyRequiredOptions(flang_cmake_args, [
+        ('-G', 'Ninja'),
+        ])
+
+    flang_obj_dir = "build_flang"
+    flang_src_dir = "%s/flang" % f.monorepo_dir
+
+    # Add LLVM_DIR and MLIR_DIR to the CMake invocation.
+    llvm_dir = "%s/lib/cmake/llvm" % f.obj_dir
+    mlir_dir = "%s/lib/cmake/mlir" % f.obj_dir
+    CmakeCommand.applyRequiredOptions(flang_cmake_args, [
+        # We actually need the paths to be relative to the source directory,
+        # otherwise find_package can't locate the config files.
+        ('-DLLVM_DIR:PATH=',
+            LLVMBuildFactory.pathRelativeTo(llvm_dir, flang_src_dir)),
+        ('-DMLIR_DIR:PATH=',
+            LLVMBuildFactory.pathRelativeTo(mlir_dir, flang_src_dir)),
+        ])
+
+    # We can't use addCmakeSteps as that would use the path in f.llvm_srcdir.
+    f.addStep(CmakeCommand(name="cmake-configure-flang",
+                           haltOnFailure=True,
+                           description=["CMake", "configure", "flang"],
+                           options=flang_cmake_args,
+                           path=LLVMBuildFactory.pathRelativeTo(flang_src_dir,
+                                                                flang_obj_dir),
+                           env=env,
+                           workdir=flang_obj_dir,
+                           **kwargs))
+
+    addNinjaSteps(
+       f,
+       obj_dir=flang_obj_dir,
+       checks=checks,
+       env=env,
+       stage_name="flang",
+       **kwargs)
+
+    return f