diff --git a/scripts/generate.py b/scripts/generate.py
index 2c4cae8..d7ded60 100644
--- a/scripts/generate.py
+++ b/scripts/generate.py
@@ -107,6 +107,7 @@ def regen_all(src_top, dest_top, *, docs=None, db=None):
     # This includes a virtual headline for ID-referenced documents.
     all_headlines = []
     main_headlines_by_path = {}
+    main_headline_to_docid = {}
     for doc in docs:
         relpath = os.path.relpath(doc.path, src_top)
         changed = False
@@ -151,6 +152,7 @@ def regen_all(src_top, dest_top, *, docs=None, db=None):
             main_headlines_by_path[doc.path] = main_headline
             if doc.id is not None:
                 doc_to_headline_remapping['id:' + doc.id] = 'id:' + main_headline.id
+                main_headline_to_docid[main_headline.id] = doc.id
                 files_generated += 1
         elif doc.id is not None:
             logging.error("Cannot render document from id: {}. {} headlines {} related".format(
@@ -159,8 +161,8 @@ def regen_all(src_top, dest_top, *, docs=None, db=None):
                 'with' if related is not None else 'without'
             ))
 
-    graph = {}
     # Build graph
+    graph = {}
     for headline in all_headlines:
         links = []
         headline_links = list(headline.get_links())
@@ -200,6 +202,8 @@ def regen_all(src_top, dest_top, *, docs=None, db=None):
             "links": links,
             "depth": headline.depth,
         }
+        if headline.id in main_headline_to_docid:
+            graph[main_headline_to_docid[headline.id]] = graph[headline.id]
 
         topLevelHeadline = headline
         while isinstance(topLevelHeadline.parent, org_rw.Headline):
@@ -306,6 +310,13 @@ def get_headline_with_name(target_name, doc):
 
     return None
 
+def assert_id_exists(id, src_headline, graph):
+    if id not in graph["nodes"]:
+        raise AssertionError("Cannot follow link to '{}' on headline '{}' ({})"
+                             .format(id,
+                                     src_headline.id,
+                                     src_headline.title.get_text()))
+
 def print_tree(tree, indentation=0, headline=None):
     # if headline and headline.id != INDEX_ID:
     #     return
@@ -437,6 +448,7 @@ def render_text_tokens(tokens, acc, headline, graph):
             link_target = chunk.value
             is_internal_link = True
             if link_target.startswith('id:'):
+                assert_id_exists(link_target[3:], headline, graph)
                 link_target = './' + link_target[3:] + '.node.html'
             elif link_target.startswith('./') or link_target.startswith('../'):
                 if '::' in link_target:
@@ -447,6 +459,7 @@ def render_text_tokens(tokens, acc, headline, graph):
                     if target_path not in graph['main_headlines']:
                         logging.warn('Link to doc not in graph: {}'.format(target_path))
                     else:
+                        assert_id_exists(graph['main_headlines'][target_path].id, headline, graph)
                         link_target = './' + graph['main_headlines'][target_path].id + '.node.html'
             elif link_target.startswith('attachment:'):
                 logging.warn('Not implemented `attachment:` links. Used on {}'.format(link_target))
@@ -455,6 +468,7 @@ def render_text_tokens(tokens, acc, headline, graph):
                 if target_headline is None:
                     logging.warn('No headline found corresponding to {}. On file {}'.format(link_target, headline.doc.path))
                 else:
+                    assert_id_exists(target_headline.id, headline, graph)
                     link_target = './' + target_headline.id + '.node.html'
             else:
                 is_internal_link = False