diff --git a/src/pyproject_fmt/formatter/project.py b/src/pyproject_fmt/formatter/project.py
index a3577d7..4020567 100644
--- a/src/pyproject_fmt/formatter/project.py
+++ b/src/pyproject_fmt/formatter/project.py
@@ -22,6 +22,7 @@
     from .config import Config
 
 _PY_MIN_VERSION: int = 7
+_ANY_WHITESPACE = re.compile(r"\s+")
 
 
 def fmt_project(parsed: TOMLDocument, conf: Config) -> None:  # noqa: C901
@@ -40,7 +41,9 @@ def fmt_project(parsed: TOMLDocument, conf: Config) -> None:  # noqa: C901
         assert isinstance(name, str)  # noqa: S101
         project["name"] = canonicalize_name(name)
     if "description" in project:
-        project["description"] = String.from_raw(str(project["description"]).strip())
+        # Convert multiline description to a single line
+        _description = _ANY_WHITESPACE.sub(" ", str(project["description"]).strip())
+        project["description"] = String.from_raw(_description, escape=False)
 
     sorted_array(cast(Optional[Array], project.get("keywords")), indent=conf.indent)
     sorted_array(cast(Optional[Array], project.get("dynamic")), indent=conf.indent)
diff --git a/tests/formatter/test_project.py b/tests/formatter/test_project.py
index 801b74a..f822a71 100644
--- a/tests/formatter/test_project.py
+++ b/tests/formatter/test_project.py
@@ -115,6 +115,19 @@ def test_project_description(fmt: Fmt) -> None:
     fmt(fmt_project, start, expected)
 
 
+def test_project_description_multiline(fmt: Fmt) -> None:
+    start = dedent('''\
+        [project]
+        description="""A multi-line
+                       description."""
+    ''')
+    expected = dedent("""\
+        [project]
+        description="A multi-line description."
+    """)
+    fmt(fmt_project, start, expected)
+
+
 def test_project_scripts(fmt: Fmt) -> None:
     start = """
     [project.scripts]