diff --git a/news/106.bugfix.md b/news/106.bugfix.md
new file mode 100644
index 0000000..f2638ec
--- /dev/null
+++ b/news/106.bugfix.md
@@ -0,0 +1 @@
+Throw a better error message when a malformed requirement is being parsed.
diff --git a/pdm/pep517/metadata.py b/pdm/pep517/metadata.py
index 5743b2b..8bc205e 100644
--- a/pdm/pep517/metadata.py
+++ b/pdm/pep517/metadata.py
@@ -241,13 +241,18 @@ def license_files(self) -> Dict[str, List[str]]:
             raise MetadataError("license-files", "Must specify 'paths' or 'globs'")
         return rv
 
-    def _convert_dependencies(self, deps: List[str]) -> List[str]:
-        return list(filter(None, map(ensure_pep440_req, deps)))
+    def _convert_dependencies(
+        self, deps: List[str], field: str = "dependencies"
+    ) -> List[str]:
+        return list(filter(None, (ensure_pep440_req(dep, field) for dep in deps)))
 
     def _convert_optional_dependencies(
         self, deps: Mapping[str, List[str]]
     ) -> Dict[str, List[str]]:
-        return {k: self._convert_dependencies(deps[k]) for k in deps}
+        return {
+            k: self._convert_dependencies(deps[k], "optional-dependencies")
+            for k in deps
+        }
 
     dependencies: MetaField[List[str]] = MetaField(
         "dependencies", _convert_dependencies
diff --git a/pdm/pep517/utils.py b/pdm/pep517/utils.py
index a197731..dbc8893 100644
--- a/pdm/pep517/utils.py
+++ b/pdm/pep517/utils.py
@@ -11,8 +11,9 @@
 
 from pdm.pep517._vendor.packaging import tags
 from pdm.pep517._vendor.packaging.markers import Marker
-from pdm.pep517._vendor.packaging.requirements import Requirement
+from pdm.pep517._vendor.packaging.requirements import InvalidRequirement, Requirement
 from pdm.pep517._vendor.packaging.version import InvalidVersion, Version
+from pdm.pep517.exceptions import MetadataError
 from pdm.pep517.macosx_platform import calculate_macosx_platform_tag
 
 
@@ -184,11 +185,15 @@ def get_abi_tag() -> Optional[str]:
         return None
 
 
-def ensure_pep440_req(req: str) -> Optional[str]:
+def ensure_pep440_req(req: str, field: str) -> Optional[str]:
     """Discard all non-PEP 440 requirements, e.g. editable VCS requirements."""
 
     if req.strip().startswith("-e"):
         return None
+    try:
+        Requirement(req)
+    except InvalidRequirement as e:
+        raise MetadataError(field, f"Invalid requirement {req!r}\n  {e}") from e
     return req
 
 
diff --git a/tests/test_metadata.py b/tests/test_metadata.py
index 3783570..e3c3222 100644
--- a/tests/test_metadata.py
+++ b/tests/test_metadata.py
@@ -273,6 +273,22 @@ def test_invalid_license_identifier() -> None:
         metadata.license_expression
 
 
+def test_invalid_requirement_strings() -> None:
+    metadata = make_metadata(
+        {
+            "description": "test package",
+            "name": "demo",
+            "dependencies": ["+abc"],
+            "optional-dependencies": {"foo": ["foo&123"]},
+        }
+    )
+    with pytest.raises(ValueError):
+        metadata.dependencies
+
+    with pytest.raises(ValueError):
+        metadata.optional_dependencies
+
+
 @pytest.mark.deprecation
 @pytest.mark.parametrize(
     "attr_name, field_name, value",