diff --git a/src/incremental/__init__.py b/src/incremental/__init__.py
index 12ec2fa..7a84a9e 100644
--- a/src/incremental/__init__.py
+++ b/src/incremental/__init__.py
@@ -503,7 +503,10 @@ def _load_pyproject_toml(toml_path, opt_in):  # type: (str, bool) -> Optional[_I
     # Do we have an affirmative opt-in to use Incremental? Otherwise
     # we must *never* raise exceptions.
     opt_in = opt_in or tool_incremental is not None
+    if not opt_in:
+        return None
 
+    # Extract the project name
     package = None
     if tool_incremental is not None and "name" in tool_incremental:
         package = tool_incremental["name"]
@@ -514,11 +517,9 @@ def _load_pyproject_toml(toml_path, opt_in):  # type: (str, bool) -> Optional[_I
         except KeyError:
             pass
     if package is None:
-        # We can't proceed without a project name, but that's only an error
-        # if [tool.incremental] is present.
-        if opt_in:
-            raise ValueError("""\
-Incremental faied to extract the package name from pyproject.toml. Specify it like:
+        # We can't proceed without a project name.
+        raise ValueError("""\
+Incremental failed to extract the package name from pyproject.toml. Specify it like:
 
     [project]
     name = "Foo"
@@ -529,29 +530,15 @@ def _load_pyproject_toml(toml_path, opt_in):  # type: (str, bool) -> Optional[_I
     name = "Foo"
 
 """)
-        else:
-            return None
-
     if not isinstance(package, str):
-        if opt_in:
-            raise TypeError(
-                "Package name must be a string, but found {}".format(type(package))
-            )
-        else:
-            return None
-
-    try:
-        path = _findPath(os.path.dirname(toml_path), package)
-    except ValueError:
-        if opt_in:
-            raise
-        else:
-            return None
+        raise TypeError(
+            "Package name must be a string, but found {}".format(type(package))
+        )
 
     return _IncrementalConfig(
         opt_in=opt_in,
         package=package,
-        path=path,
+        path=_findPath(os.path.dirname(toml_path), package),
     )
 
 
diff --git a/src/incremental/tests/test_pyproject.py b/src/incremental/tests/test_pyproject.py
index 998e0b3..939d8b8 100644
--- a/src/incremental/tests/test_pyproject.py
+++ b/src/incremental/tests/test_pyproject.py
@@ -158,11 +158,13 @@ def test_setuptoolsOptIn(self):
 
     def test_noToolIncrementalSection(self):
         """
-        The ``opt_in`` flag is false when there isn't a
-        ``[tool.incremental]`` section.
+        We don't produce config unless we find opt-in.
+
+        The ``[project]`` section doesn't imply opt-in, even if we can
+        recover the project name from it.
         """
         root = Path(self.mktemp())
-        pkg = root / "foo"
+        pkg = root / "foo"  # A valid package directory.
         pkg.mkdir(parents=True)
 
         config = self._loadToml(
@@ -171,11 +173,43 @@ def test_noToolIncrementalSection(self):
             path=root / "pyproject.toml",
         )
 
+        self.assertIsNone(config)
+
+    def test_pathNotFoundOptIn(self):
+        """
+        Once opted in, raise `ValueError` when the package root can't
+        be resolved.
+        """
+        root = Path(self.mktemp())
+        root.mkdir()  # Contains no package directory.
+
+        with self.assertRaisesRegex(ValueError, "Can't find the directory of package"):
+            self._loadToml(
+                '[project]\nname = "foo"\n',
+                opt_in=True,
+                path=root / "pyproject.toml",
+            )
+
+    def test_noToolIncrementalSectionOptIn(self):
+        """
+        If opted in (i.e. in the Hatch plugin) then the [tool.incremental]
+        table is completely optional.
+        """
+        root = Path(self.mktemp())
+        pkg = root / "src" / "foo"
+        pkg.mkdir(parents=True)
+
+        config = self._loadToml(
+            '[project]\nname = "Foo"\n',
+            opt_in=True,
+            path=root / "pyproject.toml",
+        )
+
         self.assertEqual(
             config,
             _IncrementalConfig(
-                opt_in=False,
-                package="foo",
+                opt_in=True,
+                package="Foo",
                 path=str(pkg),
             ),
         )