diff --git a/swh/indexer/metadata_dictionary/npm.py b/swh/indexer/metadata_dictionary/npm.py
--- a/swh/indexer/metadata_dictionary/npm.py
+++ b/swh/indexer/metadata_dictionary/npm.py
@@ -160,7 +160,7 @@
         >>> NpmMapping().normalize_description(None) is None
         True
         """
-        if description is None:
+        if not isinstance(description, str):
             return None
         # XXX: if this function ever need to support more cases, consider
         # switching to https://pypi.org/project/ftfy/ instead of adding more hacks
diff --git a/swh/indexer/tests/test_metadata.py b/swh/indexer/tests/test_metadata.py
--- a/swh/indexer/tests/test_metadata.py
+++ b/swh/indexer/tests/test_metadata.py
@@ -253,6 +253,30 @@
         # then
         assert declared_metadata == result
 
+    def test_compute_metadata_invalid_description_npm(self):
+        """
+        testing only computation of metadata with hard_mapping_npm
+        """
+        # given
+        content = b"""
+            {
+                "name": "test_metadata",
+                "version": "0.0.2",
+                "description": 1234
+        }
+        """
+        declared_metadata = {
+            "@context": "https://doi.org/10.5063/schema/codemeta-2.0",
+            "type": "SoftwareSourceCode",
+            "name": "test_metadata",
+            "version": "0.0.2",
+        }
+
+        # when
+        result = self.npm_mapping.translate(content)
+        # then
+        assert declared_metadata == result
+
     def test_index_content_metadata_npm(self):
         """
         testing NPM with package.json