diff -r 1970afe52da4 -r eb93feb6d3a3 tests/subfiles.py
--- a/tests/subfiles.py	Sun Jun 23 12:17:40 2019 +0300
+++ b/tests/subfiles.py	Mon Jun 24 00:28:37 2019 +0300
@@ -206,10 +206,34 @@
                 sorted_dims[-1],
             )
 
+@problem_type('bad-category',
+    severity = 'hold',
+    message = lambda category: str.format(
+        '"{category}" is not an official category',
+        category = category,
+    )
+)
+def category_test(model):
+    if model.header.valid:
+        categories = library_standards['categories'].keys()
+        if model.header.effective_category not in categories:
+            try:
+                bad_object = model.find_first_header_object('category')
+            except KeyError:
+                # category was not specified using !CATEGORY, blame
+                # the description instead
+                bad_object = model.body[0]
+            yield report_problem(
+                'bad-category',
+                bad_object = bad_object,
+                category = model.header.effective_category,
+            )
+
 manifest = {
     'tests': [
         determinant_test,
         scaling_legality_test,
         dependent_subfile_tests,
+        category_test,
     ],
 }