diff --git a/tools/unit-test-app/idf_ext.py b/tools/unit-test-app/idf_ext.py
index 13a01a311..9bc9ae007 100644
--- a/tools/unit-test-app/idf_ext.py
+++ b/tools/unit-test-app/idf_ext.py
@@ -141,12 +141,12 @@ def add_action_extensions(base_functions, base_actions):
                 # config folder to build config
                 sdkconfig_default = os.path.join(PROJECT_PATH, "sdkconfig.defaults")
 
-                with open(sdkconfig_default, "r") as sdkconfig_default_file:
+                with open(sdkconfig_default, "rb") as sdkconfig_default_file:
                     sdkconfig_temp.write(sdkconfig_default_file.read())
 
                 sdkconfig_config = os.path.join(PROJECT_PATH, "configs", config_name)
-                with open(sdkconfig_config, "r") as sdkconfig_config_file:
-                    sdkconfig_temp.write("\n")
+                with open(sdkconfig_config, "rb") as sdkconfig_config_file:
+                    sdkconfig_temp.write(b"\n")
                     sdkconfig_temp.write(sdkconfig_config_file.read())
 
                 sdkconfig_temp.flush()
@@ -276,4 +276,4 @@ idf.py ut-apply-config-NAME - Generates configuration based on configs/NAME in s
 
     extensions["ut-help"] = (ut_help, [], [])
 
-    base_actions.update(extensions)
\ No newline at end of file
+    base_actions.update(extensions)