diff --git a/src/kimi_cli/auth/oauth.py b/src/kimi_cli/auth/oauth.py
index 96d025d96..801fee3e4 100644
--- a/src/kimi_cli/auth/oauth.py
+++ b/src/kimi_cli/auth/oauth.py
@@ -195,7 +195,7 @@ def get_device_id() -> str:
 def _ascii_header_value(value: str, *, fallback: str = "unknown") -> str:
     try:
         value.encode("ascii")
-        return value
+        return value.strip()
     except UnicodeEncodeError:
         sanitized = value.encode("ascii", errors="ignore").decode("ascii").strip()
         return sanitized or fallback
diff --git a/tests/utils/test_oauth_headers.py b/tests/utils/test_oauth_headers.py
new file mode 100644
index 000000000..a1a424678
--- /dev/null
+++ b/tests/utils/test_oauth_headers.py
@@ -0,0 +1,22 @@
+from kimi_cli.auth.oauth import _ascii_header_value
+
+
+def test_ascii_header_value_strips_trailing_space():
+    assert _ascii_header_value("test ") == "test"
+    assert _ascii_header_value(" test") == "test"
+    assert _ascii_header_value("  test  ") == "test"
+
+
+def test_ascii_header_value_non_ascii_strips_trailing_space():
+    # Non-ASCII character (Chinese 'test') followed by space
+    # The non-ASCII characters are ignored by encode('ascii', errors='ignore')
+    # So "测试 " becomes " " and then .strip() makes it empty, returning fallback
+    assert _ascii_header_value("测试 ") == "unknown"
+    # "A测试 " -> "A " -> "A"
+    assert _ascii_header_value("A测试 ") == "A"
+
+
+def test_ascii_header_value_fallback():
+    # Only non-ASCII characters that get ignored, resulting in empty string
+    assert _ascii_header_value("🚀") == "unknown"
+    assert _ascii_header_value("🚀", fallback="default") == "default"