diff --git a/platformio/project/options.py b/platformio/project/options.py
index 6a6d4967..51611d24 100644
--- a/platformio/project/options.py
+++ b/platformio/project/options.py
@@ -87,8 +87,7 @@ def validate_dir(path):
         return path
     if path.startswith("~"):
         path = fs.expanduser(path)
-    return path
-    # return os.path.abspath(path)
+    return os.path.abspath(path)
 
 
 def get_default_core_dir():
diff --git a/tests/project/test_config.py b/tests/project/test_config.py
index 474033f3..06e92a32 100644
--- a/tests/project/test_config.py
+++ b/tests/project/test_config.py
@@ -354,7 +354,10 @@ def test_get_value(config):
         "--help",
     ]
     # test relative dir
-    assert config.get("platformio", "src_dir") == "source"
+    assert config.get("platformio", "src_dir") == os.path.abspath(
+        os.path.join(os.getcwd(), "source")
+    )
+
     # renamed option
     assert config.get("env:extra_1", "lib_install") == ["574"]
     assert config.get("env:extra_1", "lib_deps") == ["574"]
@@ -651,7 +654,7 @@ def test_nested_interpolation(tmp_path: Path):
         """
 [platformio]
 build_dir = /tmp/pio-$PROJECT_HASH
-data_dir = $PROJECT_DIR/assets
+data_dir = /$PROJECT_DIR/assets
 
 [env:myenv]
 build_flags = -D UTIME=${UNIX_TIME}
@@ -665,7 +668,7 @@ test_testing_command =
     """
     )
     config = ProjectConfig(str(project_conf))
-    assert config.get("platformio", "data_dir") == "$PROJECT_DIR/assets"
+    assert config.get("platformio", "data_dir") == "/$PROJECT_DIR/assets"
     assert config.get("env:myenv", "build_flags")[0][-10:].isdigit()
     testing_command = config.get("env:myenv", "test_testing_command")
     assert "$" not in " ".join(testing_command)