diff --git a/lib/ui/views/ib/builders/ib_chapter_contents_builder.dart b/lib/ui/views/ib/builders/ib_chapter_contents_builder.dart
index 34bac16..34dd680 100644
--- a/lib/ui/views/ib/builders/ib_chapter_contents_builder.dart
+++ b/lib/ui/views/ib/builders/ib_chapter_contents_builder.dart
@@ -3,6 +3,18 @@ import 'package:flutter_markdown/flutter_markdown.dart';
 import 'package:markdown/markdown.dart' as md;
 
 class IbChapterContentsBuilder extends MarkdownElementBuilder {
+  // Registers the tag as a block element, without which flutter_markdown
+  // treats it as inline and crashes on the null root block tag.
+  @override
+  bool isBlockElement() => true;
+
+  // The element's own text is metadata (an id), not content to render.
+  // Returning a widget rather than null keeps flutter_markdown from
+  // leaving an empty inline behind, which trips its end-of-build assert.
+  @override
+  Widget visitText(md.Text text, TextStyle? preferredStyle) =>
+      const SizedBox.shrink();
+
   IbChapterContentsBuilder({this.chapterContents});
 
   final Widget? chapterContents;
diff --git a/lib/ui/views/ib/builders/ib_interaction_builder.dart b/lib/ui/views/ib/builders/ib_interaction_builder.dart
index 5749240..19aff28 100644
--- a/lib/ui/views/ib/builders/ib_interaction_builder.dart
+++ b/lib/ui/views/ib/builders/ib_interaction_builder.dart
@@ -8,6 +8,18 @@ import 'package:mobile_app/viewmodels/ib/ib_page_viewmodel.dart';
 import 'package:webview_flutter/webview_flutter.dart';
 
 class IbInteractionBuilder extends MarkdownElementBuilder {
+  // Registers the tag as a block element, without which flutter_markdown
+  // treats it as inline and crashes on the null root block tag.
+  @override
+  bool isBlockElement() => true;
+
+  // The element's own text is metadata (an id), not content to render.
+  // Returning a widget rather than null keeps flutter_markdown from
+  // leaving an empty inline behind, which trips its end-of-build assert.
+  @override
+  Widget visitText(md.Text text, TextStyle? preferredStyle) =>
+      const SizedBox.shrink();
+
   IbInteractionBuilder({required this.model});
 
   final IbPageViewModel model;
diff --git a/lib/ui/views/ib/builders/ib_pop_quiz_builder.dart b/lib/ui/views/ib/builders/ib_pop_quiz_builder.dart
index 059f1ea..ac01f5f 100644
--- a/lib/ui/views/ib/builders/ib_pop_quiz_builder.dart
+++ b/lib/ui/views/ib/builders/ib_pop_quiz_builder.dart
@@ -5,6 +5,18 @@ import 'package:mobile_app/ui/views/ib/components/ib_pop_quiz.dart';
 import 'package:mobile_app/viewmodels/ib/ib_page_viewmodel.dart';
 
 class IbPopQuizBuilder extends MarkdownElementBuilder {
+  // Registers the tag as a block element, without which flutter_markdown
+  // treats it as inline and crashes on the null root block tag.
+  @override
+  bool isBlockElement() => true;
+
+  // The element's own text is metadata (an id), not content to render.
+  // Returning a widget rather than null keeps flutter_markdown from
+  // leaving an empty inline behind, which trips its end-of-build assert.
+  @override
+  Widget visitText(md.Text text, TextStyle? preferredStyle) =>
+      const SizedBox.shrink();
+
   IbPopQuizBuilder({required this.context, required this.model});
 
   final BuildContext context;
diff --git a/lib/ui/views/ib/builders/ib_webview_builder.dart b/lib/ui/views/ib/builders/ib_webview_builder.dart
index bd83ba2..5c7d8bd 100644
--- a/lib/ui/views/ib/builders/ib_webview_builder.dart
+++ b/lib/ui/views/ib/builders/ib_webview_builder.dart
@@ -5,6 +5,18 @@ import 'package:webview_flutter/webview_flutter.dart';
 import 'package:markdown/markdown.dart' as md;
 
 class IbWebViewBuilder extends MarkdownElementBuilder {
+  // Registers the tag as a block element, without which flutter_markdown
+  // treats it as inline and crashes on the null root block tag.
+  @override
+  bool isBlockElement() => true;
+
+  // The element's own text is metadata (an id), not content to render.
+  // Returning a widget rather than null keeps flutter_markdown from
+  // leaving an empty inline behind, which trips its end-of-build assert.
+  @override
+  Widget visitText(md.Text text, TextStyle? preferredStyle) =>
+      const SizedBox.shrink();
+
   IbWebViewBuilder();
 
   @override
diff --git a/lib/ui/views/ib/syntaxes/ib_md_tag_syntax.dart b/lib/ui/views/ib/syntaxes/ib_md_tag_syntax.dart
index d32346b..658327a 100644
--- a/lib/ui/views/ib/syntaxes/ib_md_tag_syntax.dart
+++ b/lib/ui/views/ib/syntaxes/ib_md_tag_syntax.dart
@@ -30,7 +30,9 @@ class IbMdTagSyntax extends md.BlockSyntax {
 
       // Eat all quiz content
       do {
-        quizContent += '\n${parser.current}';
+        // `current` is a Line, not a String — interpolating it directly
+        // yields "Instance of 'Line'" and the quiz parses as empty.
+        quizContent += '\n${parser.current.content}';
         parser.advance();
       } while (parser.next != null || !parser.isDone);