diff --git a/src/main/java/uk/org/iay/incommon/validator/api/ValidatorsApiController.java b/src/main/java/uk/org/iay/incommon/validator/api/ValidatorsApiController.java
index 8d93967..3f747e0 100644
--- a/src/main/java/uk/org/iay/incommon/validator/api/ValidatorsApiController.java
+++ b/src/main/java/uk/org/iay/incommon/validator/api/ValidatorsApiController.java
@@ -92,11 +92,17 @@ public ResponseEntity<List<Status>> validate(
                 final String validatorId,
             @ApiParam(value = "The metadata to be validated.", required = true) @Valid @RequestBody
                 final String metadata) throws ApiException {
+
+        // Fetch the required validator.
+        final ValidatorCollection.Entry entry = validatorCollection.getEntry(validatorId);
+        if (entry == null) {
+            throw new NotFoundException("unknown validator identifier '" + validatorId + "'");
+        }
+
         final List<Status> statuses = new ArrayList<>();
         statuses.add(makeStatus(StatusEnum.ERROR, "component", "message"));
         statuses.add(makeStatus(StatusEnum.WARNING, "component/sub", "another message"));
-        //return new ResponseEntity<List<Status>>(statuses, HttpStatus.NOT_IMPLEMENTED);
-        throw new NotFoundException("bad validator identifier '" + validatorId + "'");
+        return new ResponseEntity<List<Status>>(statuses, HttpStatus.NOT_IMPLEMENTED);
     }
 
     /**
diff --git a/src/main/java/uk/org/iay/incommon/validator/context/ValidatorCollection.java b/src/main/java/uk/org/iay/incommon/validator/context/ValidatorCollection.java
index ab3c6c7..310a302 100644
--- a/src/main/java/uk/org/iay/incommon/validator/context/ValidatorCollection.java
+++ b/src/main/java/uk/org/iay/incommon/validator/context/ValidatorCollection.java
@@ -100,6 +100,16 @@ public List<Entry> getEntries() {
         return entries;
     }
 
+    /**
+     * Get the {@link Entry} with the given identifier, if any.
+     *
+     * @param id the identifier for the required {@link Entry}
+     * @return the {@link Entry}, or <code>null</code>
+     */
+    public Entry getEntry(final String id) {
+        return byId.get(id);
+    }
+
     /**
      * Build an {@link ApplicationContext} from the indicated configuration,
      * and add it to the collection.