diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1196521..e3d3cc7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -39,31 +39,15 @@
 
 PROJECT(CERES C CXX)
 
+# Make CMake aware of the cmake folder for local FindXXX scripts,
+# append rather than set in case the user has passed their own
+# additional paths via -D.
+LIST(APPEND CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake")
+INCLUDE(UpdateCacheVariable)
+
 # Set up the git hook to make Gerrit Change-Id: lines in commit messages.
-SET (LOCAL_GIT_DIRECTORY)
-IF (EXISTS ${CMAKE_SOURCE_DIR}/.git)
-  # .git directory can be found on Unix based system, or on Windows with
-  # Git Bash (shipped with msysgit)
-  SET (LOCAL_GIT_DIRECTORY ${CMAKE_SOURCE_DIR}/.git)
-ELSE (EXISTS ${CMAKE_SOURCE_DIR}/.git)
-  # TODO(keir) Add proper Windows support
-ENDIF (EXISTS ${CMAKE_SOURCE_DIR}/.git)
-
-IF (EXISTS ${LOCAL_GIT_DIRECTORY})
-  IF (NOT EXISTS ${LOCAL_GIT_DIRECTORY}/hooks/commit-msg)
-    # Download the hook only if it is not already present
-    FILE(DOWNLOAD https://ceres-solver-review.googlesource.com/tools/hooks/commit-msg
-         ${CMAKE_BINARY_DIR}/commit-msg)
-
-    # Make the downloaded file executable, since it is not by default.
-    FILE(COPY ${CMAKE_BINARY_DIR}/commit-msg
-         DESTINATION ${LOCAL_GIT_DIRECTORY}/hooks/
-         FILE_PERMISSIONS
-           OWNER_READ OWNER_WRITE OWNER_EXECUTE
-           GROUP_READ GROUP_WRITE GROUP_EXECUTE
-           WORLD_READ WORLD_EXECUTE)
-  ENDIF (NOT EXISTS ${LOCAL_GIT_DIRECTORY}/hooks/commit-msg)
-ENDIF (EXISTS ${LOCAL_GIT_DIRECTORY})
+INCLUDE(AddGerritCommitHook)
+ADD_GERRIT_COMMIT_HOOK()
 
 # On OS X, add the Homebrew prefix to the set of prefixes searched by
 # CMake in find_path & find_library.  This should ensure that we can
@@ -83,12 +67,6 @@
   ENDIF()
 ENDIF()
 
-# Make CMake aware of the cmake folder for local FindXXX scripts,
-# append rather than set in case the user has passed their own
-# additional paths via -D.
-LIST(APPEND CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake")
-INCLUDE(UpdateCacheVariable)
-
 SET(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
 SET(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
 SET(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
diff --git a/cmake/AddGerritCommitHook.cmake b/cmake/AddGerritCommitHook.cmake
new file mode 100644
index 0000000..36da67a
--- /dev/null
+++ b/cmake/AddGerritCommitHook.cmake
@@ -0,0 +1,76 @@
+# Ceres Solver - A fast non-linear least squares minimizer
+# Copyright 2015 Google Inc. All rights reserved.
+# http://ceres-solver.org/
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#
+# * Redistributions of source code must retain the above copyright notice,
+#   this list of conditions and the following disclaimer.
+# * Redistributions in binary form must reproduce the above copyright notice,
+#   this list of conditions and the following disclaimer in the documentation
+#   and/or other materials provided with the distribution.
+# * Neither the name of Google Inc. nor the names of its contributors may be
+#   used to endorse or promote products derived from this software without
+#   specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+#
+# Authors: keir@google.com (Keir Mierle)
+#          alexs.mac@gmail.com (Alex Stewart)
+
+# Set up the git hook to make Gerrit Change-Id: lines in commit messages.
+FUNCTION(ADD_GERRIT_COMMIT_HOOK)
+  UNSET (LOCAL_GIT_DIRECTORY)
+  IF (EXISTS ${CMAKE_SOURCE_DIR}/.git)
+    IF (IS_DIRECTORY ${CMAKE_SOURCE_DIR}/.git)
+      # .git directory can be found on Unix based system, or on Windows with
+      # Git Bash (shipped with msysgit).
+      SET (LOCAL_GIT_DIRECTORY ${CMAKE_SOURCE_DIR}/.git)
+    ELSE(IS_DIRECTORY ${CMAKE_SOURCE_DIR}/.git)
+      # .git is a file, this means Ceres is a git submodule of another project
+      # and our .git file contains the path to the git directory which manages
+      # Ceres, so we should add the gerrit hook there.
+      FILE(READ ${CMAKE_SOURCE_DIR}/.git GIT_SUBMODULE_FILE_CONTENTS)
+      # Strip any trailing newline characters, s/t we get a valid path.
+      STRING(REGEX REPLACE "gitdir:[ ]*([^$].*)[\n].*" "${CMAKE_SOURCE_DIR}/\\1"
+        GIT_SUBMODULE_GIT_DIRECTORY_PATH "${GIT_SUBMODULE_FILE_CONTENTS}")
+      GET_FILENAME_COMPONENT(GIT_SUBMODULE_GIT_DIRECTORY_PATH
+        "${GIT_SUBMODULE_GIT_DIRECTORY_PATH}" ABSOLUTE)
+      IF (EXISTS ${GIT_SUBMODULE_GIT_DIRECTORY_PATH}
+          AND IS_DIRECTORY ${GIT_SUBMODULE_GIT_DIRECTORY_PATH})
+        SET(LOCAL_GIT_DIRECTORY "${GIT_SUBMODULE_GIT_DIRECTORY_PATH}")
+      ENDIF()
+    ENDIF()
+  ELSE (EXISTS ${CMAKE_SOURCE_DIR}/.git)
+    # TODO(keir) Add proper Windows support.
+  ENDIF (EXISTS ${CMAKE_SOURCE_DIR}/.git)
+
+  IF (EXISTS ${LOCAL_GIT_DIRECTORY})
+    IF (NOT EXISTS ${LOCAL_GIT_DIRECTORY}/hooks/commit-msg)
+      MESSAGE(STATUS "Detected Ceres being used as a git submodule, adding "
+        "commit hook for Gerrit to: ${LOCAL_GIT_DIRECTORY}")
+      # Download the hook only if it is not already present.
+      FILE(DOWNLOAD https://ceres-solver-review.googlesource.com/tools/hooks/commit-msg
+        ${CMAKE_BINARY_DIR}/commit-msg)
+
+      # Make the downloaded file executable, since it is not by default.
+      FILE(COPY ${CMAKE_BINARY_DIR}/commit-msg
+        DESTINATION ${LOCAL_GIT_DIRECTORY}/hooks/
+        FILE_PERMISSIONS
+        OWNER_READ OWNER_WRITE OWNER_EXECUTE
+        GROUP_READ GROUP_WRITE GROUP_EXECUTE
+        WORLD_READ WORLD_EXECUTE)
+    ENDIF (NOT EXISTS ${LOCAL_GIT_DIRECTORY}/hooks/commit-msg)
+  ENDIF (EXISTS ${LOCAL_GIT_DIRECTORY})
+ENDFUNCTION()