diff --git a/src/poetry/core/masonry/builders/builder.py b/src/poetry/core/masonry/builders/builder.py
index a4056a787..e0b33eead 100644
--- a/src/poetry/core/masonry/builders/builder.py
+++ b/src/poetry/core/masonry/builders/builder.py
@@ -170,13 +170,22 @@ def find_files_to_add(self, exclude_build: bool = True) -> Set["BuildIncludeFile
                 if "__pycache__" in str(file):
                     continue
 
+                if (
+                    isinstance(include, PackageInclude)
+                    and include.source
+                    and self.format == "wheel"
+                ):
+                    source_root = include.base
+                else:
+                    source_root = self._path
+
                 if file.is_dir():
                     if self.format in formats:
                         for current_file in file.glob("**/*"):
                             include_file = BuildIncludeFile(
                                 path=current_file,
                                 project_root=self._path,
-                                source_root=self._path,
+                                source_root=source_root,
                             )
 
                             if not current_file.is_dir() and not self.is_excluded(
@@ -185,15 +194,6 @@ def find_files_to_add(self, exclude_build: bool = True) -> Set["BuildIncludeFile
                                 to_add.add(include_file)
                     continue
 
-                if (
-                    isinstance(include, PackageInclude)
-                    and include.source
-                    and self.format == "wheel"
-                ):
-                    source_root = include.base
-                else:
-                    source_root = self._path
-
                 include_file = BuildIncludeFile(
                     path=file, project_root=self._path, source_root=source_root
                 )
diff --git a/tests/masonry/builders/test_complete.py b/tests/masonry/builders/test_complete.py
index 672242111..6be09a470 100644
--- a/tests/masonry/builders/test_complete.py
+++ b/tests/masonry/builders/test_complete.py
@@ -465,6 +465,32 @@ def test_package_src():
         zip.close()
 
 
+def test_split_source():
+    module_path = fixtures_dir / "split_source"
+    builder = Builder(Factory().create_poetry(module_path))
+    builder.build(fmt="all")
+
+    sdist = module_path / "dist" / "split-source-0.1.tar.gz"
+
+    assert sdist.exists()
+
+    with tarfile.open(str(sdist), "r") as tar:
+        assert "split-source-0.1/lib_a/module_a/__init__.py" in tar.getnames()
+        assert "split-source-0.1/lib_b/module_b/__init__.py" in tar.getnames()
+
+    whl = module_path / "dist" / "split_source-0.1-py3-none-any.whl"
+
+    assert whl.exists()
+
+    zip = zipfile.ZipFile(str(whl))
+
+    try:
+        assert "module_a/__init__.py" in zip.namelist()
+        assert "module_b/__init__.py" in zip.namelist()
+    finally:
+        zip.close()
+
+
 def test_package_with_include(mocker: "MockerFixture"):
     module_path = fixtures_dir / "with-include"