diff --git a/src/pyproject_installer/__main__.py b/src/pyproject_installer/__main__.py
index 22ee97c..3f60067 100644
--- a/src/pyproject_installer/__main__.py
+++ b/src/pyproject_installer/__main__.py
@@ -83,7 +83,7 @@ def wrapped(args, parser):
 
 class RunnerResult:
     def __init__(
-        self, status, message, log, exception=None, print_traceback=False
+        self, status, message, log, *, exception=None, print_traceback=False
     ):
         self.status = status
         self.message = message
diff --git a/src/pyproject_installer/deps_cmd/deps_config.py b/src/pyproject_installer/deps_cmd/deps_config.py
index 5052064..acd540a 100644
--- a/src/pyproject_installer/deps_cmd/deps_config.py
+++ b/src/pyproject_installer/deps_cmd/deps_config.py
@@ -257,6 +257,7 @@ def depformat(self, req, depformat, depformatextra):
 
     def eval(
         self,
+        *,
         srcnames=[],
         depformat=None,
         depformatextra=None,
diff --git a/src/pyproject_installer/lib/build_backend.py b/src/pyproject_installer/lib/build_backend.py
index 43c0dbc..6d81146 100644
--- a/src/pyproject_installer/lib/build_backend.py
+++ b/src/pyproject_installer/lib/build_backend.py
@@ -182,7 +182,9 @@ def parse_build_system_spec(srcdir):
     return bs
 
 
-def make_helper_args(python, result_fd, verbose, build_system, hook, hook_args):
+def make_helper_args(
+    *, python, result_fd, verbose, build_system, hook, hook_args
+):
     args = [
         python,
         BACKEND_CALLER,