diff --git a/tools/run-mypy b/tools/run-mypy
index 27ee50f..48a1ada 100755
--- a/tools/run-mypy
+++ b/tools/run-mypy
@@ -20,7 +20,6 @@ sys.path.append(os.path.dirname(TOOLS_DIR))
 
 exclude = """
 zulip/integrations/perforce/git_p4.py
-zulip/integrations/zephyr/process_ccache
 zulip/tests/__init__.py
 zulip/tests/test_default_arguments.py
 
diff --git a/zulip/integrations/zephyr/process_ccache b/zulip/integrations/zephyr/process_ccache
index 51cf78f..35f96bb 100755
--- a/zulip/integrations/zephyr/process_ccache
+++ b/zulip/integrations/zephyr/process_ccache
@@ -10,7 +10,7 @@ ccache_data_encoded = sys.argv[3]
 
 # Update the Kerberos ticket cache file
 program_name = "zmirror-%s" % (short_user,)
-with open("/home/zulip/ccache/%s" % (program_name,), "w") as f:
+with open("/home/zulip/ccache/%s" % (program_name,), "wb") as f:
     f.write(base64.b64decode(ccache_data_encoded))
 
 # Setup API key