diff --git a/locale/config.ts b/locale/config.ts
index 43667e725..33f162a5d 100644
--- a/locale/config.ts
+++ b/locale/config.ts
@@ -145,9 +145,10 @@ interface ExampleCategory {
      */
     name: string;
     /**
-     * which morphemes belong to this category. visible example sentences will contain at least one listed morpheme
+     * which morphemes belong to this category. visible example sentences will contain at least one listed morpheme.
+     * if not present, example categories must be assigned to examples using the comma-separated "categories" column in examples.tsv
      */
-    morphemes: string[];
+    morphemes?: string[];
     /**
      * whether this category is only shown in comprehensive view
      * @default false
diff --git a/src/data.ts b/src/data.ts
index 8834540c9..b7968a8aa 100644
--- a/src/data.ts
+++ b/src/data.ts
@@ -20,7 +20,10 @@ export const examples = buildList(function* () {
             Example.parse(e.null || e.singular),
             Example.parse(e.null_plural || e.plural || e.singular),
             e.isHonorific,
-            e.categories ? e.categories.split(',').map(c => c.trim()).filter(c => c) : [],
+            e.categories
+                ? e.categories.split(',').map((c) => c.trim())
+                        .filter((c) => c)
+                : [],
         );
     }
 });