diff --git a/data_descriptors/activity/_schema_ b/data_descriptors/activity/_schema_
index c514e6a5..62227435 100644
--- a/data_descriptors/activity/_schema_
+++ b/data_descriptors/activity/_schema_
@@ -33,22 +33,28 @@
             "description": "A URL providing further documentation or references.",
             "format": "uri"
         },
-        "permissable": [
-            "pmip",
-            "c4mip",
-            "ramip",
-            "lmip",
-            "dcpp",
-            "aerchemmip",
-            "cfmip",
-            "rfmip",
-            "damip",
-            "cmip",
-            "lesfmip",
-            "geomip",
-            "tipmip",
-            "scenariomip"
-        ]
+        "permissable": {
+            "type": "array",
+            "items": {
+                "type": "string",
+                "enum": [
+                    "pmip",
+                    "c4mip",
+                    "ramip",
+                    "lmip",
+                    "dcpp",
+                    "aerchemmip",
+                    "cfmip",
+                    "rfmip",
+                    "damip",
+                    "cmip",
+                    "lesfmip",
+                    "geomip",
+                    "tipmip",
+                    "scenariomip"
+                ]
+            }
+        }
     },
     "required": [
         "@context",