diff --git a/test/functional/test_runner.py b/test/functional/test_runner.py
index bee96227093..714298e2e88 100755
--- a/test/functional/test_runner.py
+++ b/test/functional/test_runner.py
@@ -569,7 +569,6 @@ def main():
 
     run_tests(
         test_list=test_list,
-        src_dir=config["environment"]["SRCDIR"],
         build_dir=config["environment"]["BUILDDIR"],
         tmpdir=tmpdir,
         jobs=args.jobs,
@@ -581,7 +580,7 @@ def main():
         results_filepath=results_filepath,
     )
 
-def run_tests(*, test_list, src_dir, build_dir, tmpdir, jobs=1, enable_coverage=False, args=None, combined_logs_len=0, failfast=False, use_term_control, results_filepath=None):
+def run_tests(*, test_list, build_dir, tmpdir, jobs=1, enable_coverage=False, args=None, combined_logs_len=0, failfast=False, use_term_control, results_filepath=None):
     args = args or []
 
     # Warn if bitcoind is already running
@@ -604,7 +603,7 @@ def run_tests(*, test_list, src_dir, build_dir, tmpdir, jobs=1, enable_coverage=
         print(f"{BOLD[1]}WARNING!{BOLD[0]} There may be insufficient free space in {tmpdir} to run the Bitcoin functional test suite. "
               f"Running the test suite with fewer than {min_space // (1024 * 1024)} MB of free space might cause tests to fail.")
 
-    tests_dir = build_dir + '/test/functional/'
+    tests_dir = f"{build_dir}/test/functional/"
     # This allows `test_runner.py` to work from an out-of-source build directory using a symlink,
     # a hard link or a copy on any platform. See https://github.com/bitcoin/bitcoin/pull/27561.
     sys.path.append(tests_dir)