diff --git a/poetry/core/masonry/builders/builder.py b/poetry/core/masonry/builders/builder.py
index 04f12252c..513c26960 100644
--- a/poetry/core/masonry/builders/builder.py
+++ b/poetry/core/masonry/builders/builder.py
@@ -53,7 +53,13 @@ def __init__(
 
         packages = []
         for p in self._package.packages:
-            formats = p.get("format", [])
+            formats = p.get("format") or None
+
+            # Default to including the package in both sdist & wheel
+            # if the `format` key is not provided in the inline include table.
+            if formats is None:
+                formats = ["sdist", "wheel"]
+
             if not isinstance(formats, list):
                 formats = [formats]
 
diff --git a/tests/masonry/builders/fixtures/with_include_inline_table/both.txt b/tests/masonry/builders/fixtures/with_include_inline_table/both.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/tests/masonry/builders/fixtures/with_include_inline_table/pyproject.toml b/tests/masonry/builders/fixtures/with_include_inline_table/pyproject.toml
index 95b0949c6..5309992f1 100644
--- a/tests/masonry/builders/fixtures/with_include_inline_table/pyproject.toml
+++ b/tests/masonry/builders/fixtures/with_include_inline_table/pyproject.toml
@@ -24,6 +24,7 @@ packages = [
 
 include = [
     { path = "tests", format = "sdist" },
+    { path = "both.txt" },
     { path = "wheel_only.txt", format = "wheel" }
 ]
 
diff --git a/tests/masonry/builders/test_sdist.py b/tests/masonry/builders/test_sdist.py
index 3cb2a3b12..b67be206c 100644
--- a/tests/masonry/builders/test_sdist.py
+++ b/tests/masonry/builders/test_sdist.py
@@ -529,6 +529,7 @@ def test_includes_with_inline_table():
     assert sdist.exists()
 
     with tarfile.open(str(sdist), "r") as tar:
+        assert "with-include-1.2.3/both.txt" in tar.getnames()
         assert "with-include-1.2.3/wheel_only.txt" not in tar.getnames()
         assert "with-include-1.2.3/tests/__init__.py" in tar.getnames()
         assert "with-include-1.2.3/tests/test_foo/test.py" in tar.getnames()
diff --git a/tests/masonry/builders/test_wheel.py b/tests/masonry/builders/test_wheel.py
index 3db7c04d4..9a54ea9f2 100644
--- a/tests/masonry/builders/test_wheel.py
+++ b/tests/masonry/builders/test_wheel.py
@@ -182,6 +182,7 @@ def test_wheel_includes_inline_table():
     assert whl.exists()
 
     with zipfile.ZipFile(str(whl)) as z:
+        assert "both.txt" in z.namelist()
         assert "wheel_only.txt" in z.namelist()
         assert "notes.txt" not in z.namelist()