diff --git a/python/utils/platform_helper.py b/python/utils/platform_helper.py
index 758735b..fbc0426 100644
--- a/python/utils/platform_helper.py
+++ b/python/utils/platform_helper.py
@@ -188,7 +188,10 @@ class PlatformHelper:
             # Use XDG Base Directory specification
             xdg_config = os.environ.get("XDG_CONFIG_HOME")
             if xdg_config:
-                return Path(xdg_config) / "kicad-mcp"
+                xdg_config_path = Path(xdg_config).expanduser()
+                if xdg_config_path.is_absolute():
+                    return xdg_config_path / "kicad-mcp"
+                logger.warning("Ignoring relative XDG_CONFIG_HOME: %s", xdg_config)
             return Path.home() / ".config" / "kicad-mcp"
         elif PlatformHelper.is_macos():
             return Path.home() / "Library" / "Application Support" / "kicad-mcp"
@@ -225,7 +228,10 @@ class PlatformHelper:
         elif PlatformHelper.is_linux():
             xdg_cache = os.environ.get("XDG_CACHE_HOME")
             if xdg_cache:
-                return Path(xdg_cache) / "kicad-mcp"
+                xdg_cache_path = Path(xdg_cache).expanduser()
+                if xdg_cache_path.is_absolute():
+                    return xdg_cache_path / "kicad-mcp"
+                logger.warning("Ignoring relative XDG_CACHE_HOME: %s", xdg_cache)
             return Path.home() / ".cache" / "kicad-mcp"
         elif PlatformHelper.is_macos():
             return Path.home() / "Library" / "Caches" / "kicad-mcp"
diff --git a/tests/test_platform_helper.py b/tests/test_platform_helper.py
index b990232..f242999 100644
--- a/tests/test_platform_helper.py
+++ b/tests/test_platform_helper.py
@@ -89,6 +89,24 @@ class TestPathGeneration:
             expected = Path.home() / "Library" / "Application Support" / "kicad-mcp"
             assert config_dir == expected
 
+    def test_config_dir_ignores_relative_xdg_config_home(self, monkeypatch):
+        """Relative XDG_CONFIG_HOME should be ignored on Linux."""
+        monkeypatch.setattr(PlatformHelper, "is_linux", staticmethod(lambda: True))
+        monkeypatch.setattr(PlatformHelper, "is_windows", staticmethod(lambda: False))
+        monkeypatch.setattr(PlatformHelper, "is_macos", staticmethod(lambda: False))
+        monkeypatch.setenv("XDG_CONFIG_HOME", "relative/path")
+
+        assert PlatformHelper.get_config_dir() == Path.home() / ".config" / "kicad-mcp"
+
+    def test_cache_dir_ignores_relative_xdg_cache_home(self, monkeypatch):
+        """Relative XDG_CACHE_HOME should be ignored on Linux."""
+        monkeypatch.setattr(PlatformHelper, "is_linux", staticmethod(lambda: True))
+        monkeypatch.setattr(PlatformHelper, "is_windows", staticmethod(lambda: False))
+        monkeypatch.setattr(PlatformHelper, "is_macos", staticmethod(lambda: False))
+        monkeypatch.setenv("XDG_CACHE_HOME", "relative/cache")
+
+        assert PlatformHelper.get_cache_dir() == Path.home() / ".cache" / "kicad-mcp"
+
     def test_python_executable_is_valid(self):
         """Test that Python executable path is valid"""
         exe = PlatformHelper.get_python_executable()