diff --git a/pyproject.toml b/pyproject.toml
index be62abe..8f0eef5 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -52,6 +52,9 @@ select = [
 target-version = "py37"
 ignore = ["C901"]
 
+[tool.ruff.isort]
+known-first-party = ["pyproject_dependencies"]
+
 # coverage
 
 [tool.coverage.run]
diff --git a/src/pyproject_dependencies/__main__.py b/src/pyproject_dependencies/__main__.py
index f831dbf..1027c2a 100644
--- a/src/pyproject_dependencies/__main__.py
+++ b/src/pyproject_dependencies/__main__.py
@@ -15,11 +15,11 @@
 
 from .compat import tomllib
 
-extra_marker_re = re.compile(r"extra\s*==")
+extra_marker_re = re.compile(r".+extra\s*==")
 
 
 def _dep_has_extra(dep: str) -> bool:
-    return bool(extra_marker_re.search(dep))
+    return bool(extra_marker_re.match(dep))
 
 
 def subprocess_runner(
diff --git a/tests/test_utils.py b/tests/test_utils.py
new file mode 100644
index 0000000..cae0805
--- /dev/null
+++ b/tests/test_utils.py
@@ -0,0 +1,17 @@
+import pytest
+
+from pyproject_dependencies.__main__ import _dep_has_extra
+
+
+@pytest.mark.parametrize(
+    ("dep", "expected"),
+    [
+        ("stuff", False),
+        ("stuff[extra]", False),
+        ("stuff==1.0", False),
+        ("extra==1.0", False),
+        ("stuff>=1; extra == 'test'", True),
+    ],
+)
+def test_dep_has_extras(dep: str, expected: bool) -> None:
+    assert _dep_has_extra(dep) is expected