diff --git a/news/1274.bugfix.md b/news/1274.bugfix.md
new file mode 100644
index 0000000000000000000000000000000000000000..354d2f4a40796ee1006eacde44b70f2db796b493
--- /dev/null
+++ b/news/1274.bugfix.md
@@ -0,0 +1 @@
+For packages that are only available as source distribution, the `summary` field in `pdm.lock` contains the `description` from the package's `pyproject.toml`.
diff --git a/pdm/models/candidates.py b/pdm/models/candidates.py
index 77ced6cab21f1fbd7e6118b80ca822ca49e5c95a..4a52350f98f5e500c002c3d4789beff36722080e 100644
--- a/pdm/models/candidates.py
+++ b/pdm/models/candidates.py
@@ -443,6 +443,7 @@ class PreparedCandidate:
                 ):
                     setup = Setup(
                         name=metadata.name,
+                        summary=metadata.description,
                         version=metadata.version,
                         install_requires=metadata.dependencies or [],
                         extras_require=metadata.optional_dependencies or {},
diff --git a/pdm/models/setup.py b/pdm/models/setup.py
index 1f1bda6cb3a1c962a4dad0a90485dad0b2dd4c12..00da7cb59f87f65b7acf6348fdb964ef3bb38054 100644
--- a/pdm/models/setup.py
+++ b/pdm/models/setup.py
@@ -1,6 +1,6 @@
 import ast
 from configparser import ConfigParser
-from dataclasses import asdict, dataclass, field
+from dataclasses import asdict, dataclass, field, fields
 from pathlib import Path
 from typing import Any, Dict, Iterable, List, Optional, Tuple, no_type_check
 
@@ -16,18 +16,13 @@ class Setup:
     install_requires: List[str] = field(default_factory=list)
     extras_require: Dict[str, List[str]] = field(default_factory=dict)
     python_requires: Optional[str] = None
+    summary: Optional[str] = None
 
     def update(self, other: "Setup") -> None:
-        if other.name:
-            self.name = other.name
-        if other.version:
-            self.version = other.version
-        if other.install_requires:
-            self.install_requires = other.install_requires
-        if other.extras_require:
-            self.extras_require = other.extras_require
-        if other.python_requires:
-            self.python_requires = other.python_requires
+        for f in fields(self):
+            other_field = getattr(other, f.name)
+            if other_field:
+                setattr(self, f.name, other_field)
 
     def as_dict(self) -> Dict[str, Any]:
         return asdict(self)
diff --git a/pdm/project/metadata.py b/pdm/project/metadata.py
index 5fa1d1f17c532fe0bb2a5dae3dcd66e0f49cb233..65cb87107aae1a8f1083db822ca06b28cafba389 100644
--- a/pdm/project/metadata.py
+++ b/pdm/project/metadata.py
@@ -76,7 +76,7 @@ class SetupDistribution(Distribution):
         return {
             "Name": self._data.name,
             "Version": self._data.version,
-            "Summary": "UNKNOWN",
+            "Summary": self._data.summary,
             "Requires-Python": self._data.python_requires,
         }
 
diff --git a/tests/models/test_candidates.py b/tests/models/test_candidates.py
index 3e1f3ab011342b65a6240b83ea80bbedde48d203..1fa0d93c46228ed06ca6c85fdd9fdb034a909bc0 100644
--- a/tests/models/test_candidates.py
+++ b/tests/models/test_candidates.py
@@ -342,8 +342,9 @@ def test_parse_metadata_from_pep621(project, mocker):
         f"test-hatch @ file://{FIXTURES.as_posix()}/projects/test-hatch-static"
     )
     candidate = Candidate(req)
-    metadata = candidate.prepare(project.environment).metadata
-    assert sorted(metadata.requires) == ["click", "requests"]
+    distribution = candidate.prepare(project.environment).metadata
+    assert sorted(distribution.requires) == ["click", "requests"]
+    assert distribution.metadata["Summary"] == "Test hatch project"
     builder.assert_not_called()