diff --git a/contrib/devtools/copyright_header.py b/contrib/devtools/copyright_header.py
--- a/contrib/devtools/copyright_header.py
+++ b/contrib/devtools/copyright_header.py
@@ -54,17 +54,25 @@
 ##########################################################################
 
 
-GIT_LS_CMD = 'git ls-files'
+GIT_LS_CMD = 'git ls-files --full-name'.split(' ')
+GIT_TOPLEVEL_CMD = 'git rev-parse --show-toplevel'.split(' ')
 
 
-def call_git_ls():
-    out = subprocess.check_output(GIT_LS_CMD.split(' '))
+def call_git_ls(base_directory):
+    out = subprocess.check_output([*GIT_LS_CMD, base_directory])
     return [f for f in out.decode("utf-8").split('\n') if f != '']
 
 
-def get_filenames_to_examine():
-    filenames = call_git_ls()
-    return sorted([filename for filename in filenames if
+def call_git_toplevel():
+    "Returns the absolute path to the project root"
+    return subprocess.check_output(GIT_TOPLEVEL_CMD).strip().decode("utf-8")
+
+
+def get_filenames_to_examine(base_directory):
+    "Returns an array of absolute paths to any project files in the base_directory that pass the include/exclude filters"
+    root = call_git_toplevel()
+    filenames = call_git_ls(base_directory)
+    return sorted([os.path.join(root, filename) for filename in filenames if
                    applies_to_file(filename)])
 
 ##########################################################################
@@ -162,7 +170,7 @@
 
 
 def read_file(filename):
-    return open(os.path.abspath(filename), 'r', encoding="utf8").read()
+    return open(filename, 'r', encoding="utf8").read()
 
 
 def gather_file_info(filename):
@@ -282,12 +290,9 @@
 
 
 def exec_report(base_directory, verbose):
-    original_cwd = os.getcwd()
-    os.chdir(base_directory)
-    filenames = get_filenames_to_examine()
+    filenames = get_filenames_to_examine(base_directory)
     file_infos = [gather_file_info(f) for f in filenames]
     print_report(file_infos, verbose)
-    os.chdir(original_cwd)
 
 ##########################################################################
 # report cmd
@@ -354,14 +359,14 @@
 
 
 def read_file_lines(filename):
-    f = open(os.path.abspath(filename), 'r', encoding="utf8")
+    f = open(filename, 'r', encoding="utf8")
     file_lines = f.readlines()
     f.close()
     return file_lines
 
 
 def write_file_lines(filename, file_lines):
-    f = open(os.path.abspath(filename), 'w', encoding="utf8")
+    f = open(filename, 'w', encoding="utf8")
     f.write(''.join(file_lines))
     f.close()
 
@@ -450,11 +455,8 @@
 
 
 def exec_update_header_year(base_directory):
-    original_cwd = os.getcwd()
-    os.chdir(base_directory)
-    for filename in get_filenames_to_examine():
+    for filename in get_filenames_to_examine(base_directory):
         update_updatable_copyright(filename)
-    os.chdir(original_cwd)
 
 ##########################################################################
 # update cmd