diff --git a/buildkite/bazelci.py b/buildkite/bazelci.py
index f99a88f..65eaf15 100644
--- a/buildkite/bazelci.py
+++ b/buildkite/bazelci.py
@@ -222,14 +222,13 @@
         }
     }
 
-
-def python_binary():
-    if is_windows():
+def python_binary(platform=None):
+    if platform == "windows":
         return "python.exe"
     return "python3.6"
 
 def is_windows():
-    return os.name == 'nt'
+    return os.name == "nt"
 
 def gsutil_command():
     if is_windows():
@@ -815,7 +814,7 @@
 
 def runner_step(platform, project_name=None, http_config=None,
                 git_repository=None, use_but=False):
-    command = python_binary() + \
+    command = python_binary(platform) + \
         " bazelci.py runner --platform=" + platform
     if http_config:
         command += " --http_config=" + http_config
@@ -890,7 +889,7 @@
 
 
 def bazel_build_step(platform, project_name, http_config=None, build_only=False, test_only=False):
-    pipeline_command = python_binary() + " bazelci.py runner"
+    pipeline_command = python_binary(platform) + " bazelci.py runner"
     if build_only:
         pipeline_command += " --build_only --save_but"
     if test_only: