diff --git a/npe2/manifest/_package_metadata.py b/npe2/manifest/_package_metadata.py
index fdb3fb87..d2af3c13 100644
--- a/npe2/manifest/_package_metadata.py
+++ b/npe2/manifest/_package_metadata.py
@@ -174,7 +174,11 @@ class Config:
     def _validate_root(cls, values):
         if "metadata_version" not in values:
             fields = cls.__fields__
-            mins = {fields[n].field_info.extra.get("min_ver", "1.0") for n in values}
+            mins = {
+                fields[n].field_info.extra.get("min_ver", "1.0")
+                for n in values
+                if n in fields
+            }
             values["metadata_version"] = str(max(float(x) for x in mins))
         return values
 
diff --git a/tests/test_package_meta.py b/tests/test_package_meta.py
index 5b178909..fab9f823 100644
--- a/tests/test_package_meta.py
+++ b/tests/test_package_meta.py
@@ -17,3 +17,24 @@ def test_package_metadata_version():
 
 def test_hashable():
     hash(PackageMetadata(name="test", version="1.0"))
+
+
+def test_package_metadata_extra_field():
+    pkg = {
+        "name": "test",
+        "version": "1.0",
+        "maintainer": "bob",
+        "extra_field_that_is_definitely_not_in_the_model": False,
+    }
+
+    try:
+        p = PackageMetadata(**pkg)
+    except Exception:
+        raise AssertionError(
+            "failed to parse PackageMetadata from a dict with an extra field"
+        )
+
+    assert p.name == "test"
+    assert p.version == "1.0"
+    assert p.maintainer == "bob"
+    assert not hasattr(p, "extra_field_that_is_definitely_not_in_the_model")