diff --git a/swh/indexer/metadata_dictionary/codemeta.py b/swh/indexer/metadata_dictionary/codemeta.py
--- a/swh/indexer/metadata_dictionary/codemeta.py
+++ b/swh/indexer/metadata_dictionary/codemeta.py
@@ -5,6 +5,7 @@
 
 import collections
 import json
+import logging
 import re
 from typing import Any, Dict, List, Optional, Tuple, Union
 import xml.etree.ElementTree as ET
@@ -22,6 +23,8 @@
 _IGNORED_NAMESPACES = ("http://www.w3.org/2005/Atom",)
 _DATE_RE = re.compile("^[0-9]{4}-[0-9]{1,2}-[0-9]{1,2}$")
 
+logger = logging.getLogger(__name__)
+
 
 class CodemetaMapping(SingleFileIntrinsicMapping):
     """
@@ -64,7 +67,12 @@
         return [term for term in CODEMETA_TERMS if not term.startswith("@")]
 
     def xml_to_jsonld(self, e: ET.Element) -> Union[str, Dict[str, Any]]:
+        # Keys are JSON-LD property names (URIs or terms).
+        # Values are either a single string (if key is "type") or list of
+        # other dicts with the same type recursively.
+        # To simply annotations, we omit the single string case here.
         doc: Dict[str, List[Union[str, Dict[str, Any]]]] = collections.defaultdict(list)
+
         for child in e:
             m = _TAG_RE.match(child.tag)
             assert m, f"Tag with no namespace: {child}"
@@ -100,7 +108,27 @@
                     # to be allowed by the deposit; so we need to reformat them
                     # to be valid ISO8601.
                     jsonld_child = iso8601.parse_date(jsonld_child).date().isoformat()
-                doc[localname].append(jsonld_child)
+                if localname == "id":
+                    # JSON-LD only allows a single id, and they have to be strings.
+                    if localname in doc:
+                        logger.error(
+                            "Duplicate <id>s in SWORD document: %r and %r",
+                            doc[localname],
+                            jsonld_child,
+                        )
+                        continue
+                    elif not jsonld_child:
+                        logger.error("Empty <id> value in SWORD document")
+                        continue
+                    elif not isinstance(jsonld_child, str):
+                        logger.error(
+                            "Unexpected <id> value in SWORD document: %r", jsonld_child
+                        )
+                        continue
+                    else:
+                        doc[localname] = jsonld_child  # type: ignore[assignment]
+                else:
+                    doc[localname].append(jsonld_child)
             else:
                 # Otherwise, we already know the URI
                 doc[f"{namespace}{localname}"].append(self.xml_to_jsonld(child))
diff --git a/swh/indexer/tests/metadata_dictionary/test_codemeta.py b/swh/indexer/tests/metadata_dictionary/test_codemeta.py
--- a/swh/indexer/tests/metadata_dictionary/test_codemeta.py
+++ b/swh/indexer/tests/metadata_dictionary/test_codemeta.py
@@ -6,6 +6,7 @@
 import json
 
 from hypothesis import HealthCheck, given, settings
+import pytest
 
 from swh.indexer.codemeta import CODEMETA_TERMS
 from swh.indexer.metadata_detector import detect_metadata
@@ -254,6 +255,117 @@
     }
 
 
+@pytest.mark.parametrize("id_", ["", " ", "\n"])
+def test_sword_invalid_id(id_):
+    content = f"""<?xml version="1.0"?>
+    <atom:entry xmlns:atom="http://www.w3.org/2005/Atom"
+                xmlns="https://doi.org/10.5063/schema/codemeta-2.0"
+                xmlns:schema="http://schema.org/">
+      <name>My Software</name>
+      <id>{id_}</id>
+    </atom:entry>
+    """
+
+    result = MAPPINGS["SwordCodemetaMapping"]().translate(content)
+    assert result == {
+        "@context": "https://doi.org/10.5063/schema/codemeta-2.0",
+        "name": "My Software",
+    }
+
+
+@pytest.mark.parametrize(
+    "id_",
+    [
+        "foo",
+        "42",
+        "http://example.org/",
+        "http://example.org/foo",
+        "https://example.org/",
+        "https://example.org/foo",
+    ],
+)
+def test_sword_id(id_):
+    content = f"""<?xml version="1.0"?>
+    <atom:entry xmlns:atom="http://www.w3.org/2005/Atom"
+                xmlns="https://doi.org/10.5063/schema/codemeta-2.0"
+                xmlns:schema="http://schema.org/">
+      <name>My Software</name>
+      <id>{id_}</id>
+    </atom:entry>
+    """
+
+    result = MAPPINGS["SwordCodemetaMapping"]().translate(content)
+    assert result == {
+        "@context": "https://doi.org/10.5063/schema/codemeta-2.0",
+        "id": id_,
+        "name": "My Software",
+    }
+
+
+def test_sword_multiple_ids():
+    """JSON-LD only allows a single id, so we ignore all but the first one."""
+    content = """<?xml version="1.0"?>
+    <atom:entry xmlns:atom="http://www.w3.org/2005/Atom"
+                xmlns="https://doi.org/10.5063/schema/codemeta-2.0"
+                xmlns:schema="http://schema.org/">
+      <name>My Software</name>
+      <id>http://example.org/foo</id>
+      <id>http://example.org/bar</id>
+    </atom:entry>
+    """
+
+    result = MAPPINGS["SwordCodemetaMapping"]().translate(content)
+    assert result == {
+        "@context": "https://doi.org/10.5063/schema/codemeta-2.0",
+        "id": "http://example.org/foo",
+        "name": "My Software",
+    }
+
+
+def test_sword_type():
+    content = """<?xml version="1.0"?>
+    <atom:entry xmlns:atom="http://www.w3.org/2005/Atom"
+                xmlns="https://doi.org/10.5063/schema/codemeta-2.0"
+                xmlns:schema="http://schema.org/">
+      <name>My Software</name>
+      <type>http://schema.org/WebSite</type>
+    </atom:entry>
+    """
+
+    result = MAPPINGS["SwordCodemetaMapping"]().translate(content)
+    assert result == {
+        "@context": "https://doi.org/10.5063/schema/codemeta-2.0",
+        "type": "schema:WebSite",
+        "name": "My Software",
+    }
+
+
+def test_sword_multiple_type():
+    content = """<?xml version="1.0"?>
+    <atom:entry xmlns:atom="http://www.w3.org/2005/Atom"
+                xmlns="https://doi.org/10.5063/schema/codemeta-2.0"
+                xmlns:schema="http://schema.org/">
+      <name>My Software</name>
+      <type>http://schema.org/WebSite</type>
+      <type>http://schema.org/SoftwareSourceCode</type>
+    </atom:entry>
+    """
+
+    result = MAPPINGS["SwordCodemetaMapping"]().translate(content)
+    assert result in (
+        {
+            "@context": "https://doi.org/10.5063/schema/codemeta-2.0",
+            "type": ["schema:WebSite", "SoftwareSourceCode"],
+            "name": "My Software",
+        },
+        {
+            "@context": "https://doi.org/10.5063/schema/codemeta-2.0",
+            "type": ["SoftwareSourceCode", "schema:WebSite"],
+            "name": "My Software",
+        },
+    )
+
+
 def test_sword_schemaorg_in_codemeta():
     content = """<?xml version="1.0"?>
     <atom:entry xmlns:atom="http://www.w3.org/2005/Atom"