diff --git a/package.json b/package.json
index 38cf8b04..9d025019 100644
--- a/package.json
+++ b/package.json
@@ -159,6 +159,7 @@
     "slug": "^0.9.1",
     "unified": "^6.1.4",
     "unist-builder": "^1.0.2",
+    "unist-util-visit-parents": "^1.1.1",
     "uuid": "^2.0.3",
     "whatwg-fetch": "^1.0.0"
   },
diff --git a/src/components/Widgets/Markdown/serializers/__tests__/remarkAssertParents.spec.js b/src/components/Widgets/Markdown/serializers/__tests__/remarkAssertParents.spec.js
new file mode 100644
index 00000000..afccd2ed
--- /dev/null
+++ b/src/components/Widgets/Markdown/serializers/__tests__/remarkAssertParents.spec.js
@@ -0,0 +1,204 @@
+import u from 'unist-builder';
+import remarkAssertParents from '../remarkAssertParents';
+
+const transform = remarkAssertParents();
+
+describe('remarkAssertParents', () => {
+  it('should unnest invalidly nested blocks', () => {
+    const input = u('root', [
+      u('paragraph', [
+        u('paragraph', [ u('text', 'Paragraph text.') ]),
+        u('heading', { depth: 1 }, [ u('text', 'Heading text.') ]),
+        u('code', 'someCode()'),
+        u('blockquote', [ u('text', 'Quote text.') ]),
+        u('list', [ u('listItem', [ u('text', 'A list item.') ]) ]),
+        u('table', [ u('tableRow', [ u('tableCell', [ u('text', 'Text in a table cell.') ]) ]) ]),
+        u('thematicBreak'),
+      ]),
+    ]);
+
+    const output = u('root', [
+      u('paragraph', [ u('text', 'Paragraph text.') ]),
+      u('heading', { depth: 1 }, [ u('text', 'Heading text.') ]),
+      u('code', 'someCode()'),
+      u('blockquote', [ u('text', 'Quote text.') ]),
+      u('list', [ u('listItem', [ u('text', 'A list item.') ]) ]),
+      u('table', [ u('tableRow', [ u('tableCell', [ u('text', 'Text in a table cell.') ]) ]) ]),
+      u('thematicBreak'),
+    ]);
+
+    expect(transform(input)).toEqual(output);
+  });
+
+  it('should unnest deeply nested blocks', () => {
+    const input = u('root', [
+      u('paragraph', [
+        u('paragraph', [
+          u('paragraph', [
+            u('paragraph', [ u('text', 'Paragraph text.') ]),
+            u('heading', { depth: 1 }, [ u('text', 'Heading text.') ]),
+            u('code', 'someCode()'),
+            u('blockquote', [
+              u('paragraph', [
+                u('strong', [
+                  u('heading', [
+                    u('text', 'Quote text.'),
+                  ]),
+                ]),
+              ]),
+            ]),
+            u('list', [ u('listItem', [ u('text', 'A list item.') ]) ]),
+            u('table', [ u('tableRow', [ u('tableCell', [ u('text', 'Text in a table cell.') ]) ]) ]),
+            u('thematicBreak'),
+          ]),
+        ]),
+      ]),
+    ]);
+
+    const output = u('root', [
+      u('paragraph', [ u('text', 'Paragraph text.') ]),
+      u('heading', { depth: 1 }, [ u('text', 'Heading text.') ]),
+      u('code', 'someCode()'),
+      u('blockquote', [
+        u('heading', [
+          u('text', 'Quote text.'),
+        ]),
+      ]),
+      u('list', [ u('listItem', [ u('text', 'A list item.') ]) ]),
+      u('table', [ u('tableRow', [ u('tableCell', [ u('text', 'Text in a table cell.') ]) ]) ]),
+      u('thematicBreak'),
+    ]);
+
+    expect(transform(input)).toEqual(output);
+  });
+
+  it('should remove blocks that are emptied as a result of denesting', () => {
+    const input = u('root', [
+      u('paragraph', [
+        u('heading', { depth: 1 }, [ u('text', 'Heading text.') ]),
+      ]),
+    ]);
+
+    const output = u('root', [
+      u('heading', { depth: 1 }, [ u('text', 'Heading text.') ]),
+    ]);
+
+    expect(transform(input)).toEqual(output);
+  });
+
+  it('should remove blocks that are emptied as a result of denesting', () => {
+    const input = u('root', [
+      u('paragraph', [
+        u('heading', { depth: 1 }, [ u('text', 'Heading text.') ]),
+      ]),
+    ]);
+
+    const output = u('root', [
+      u('heading', { depth: 1 }, [ u('text', 'Heading text.') ]),
+    ]);
+
+    expect(transform(input)).toEqual(output);
+  });
+
+  it('should handle assymetrical splits', () => {
+    const input = u('root', [
+      u('paragraph', [
+        u('heading', { depth: 1 }, [ u('text', 'Heading text.') ]),
+      ]),
+    ]);
+
+    const output = u('root', [
+      u('heading', { depth: 1 }, [ u('text', 'Heading text.') ]),
+    ]);
+
+    expect(transform(input)).toEqual(output);
+  });
+
+  it('should nest invalidly nested blocks in the nearest valid ancestor', () => {
+    const input = u('root', [
+      u('paragraph', [
+        u('blockquote', [
+          u('strong', [
+            u('heading', { depth: 1 }, [ u('text', 'Heading text.') ]),
+          ]),
+        ]),
+      ]),
+    ]);
+
+    const output = u('root', [
+      u('blockquote', [
+        u('heading', { depth: 1 }, [ u('text', 'Heading text.') ]),
+      ]),
+    ]);
+
+    expect(transform(input)).toEqual(output);
+  });
+
+  it('should preserve validly nested siblings of invalidly nested blocks', () => {
+    const input = u('root', [
+      u('paragraph', [
+        u('blockquote', [
+          u('strong', [
+            u('text', 'Deep validly nested text a.'),
+            u('heading', { depth: 1 }, [ u('text', 'Heading text.') ]),
+            u('text', 'Deep validly nested text b.'),
+          ]),
+        ]),
+        u('text', 'Validly nested text.'),
+      ]),
+    ]);
+
+    const output = u('root', [
+      u('blockquote', [
+        u('strong', [
+          u('text', 'Deep validly nested text a.'),
+        ]),
+        u('heading', { depth: 1 }, [ u('text', 'Heading text.') ]),
+        u('strong', [
+          u('text', 'Deep validly nested text b.'),
+        ]),
+      ]),
+      u('paragraph', [
+        u('text', 'Validly nested text.'),
+      ]),
+    ]);
+
+    expect(transform(input)).toEqual(output);
+  });
+
+  it('should allow intermediate parents like list and table to contain required block children', () => {
+    const input = u('root', [
+      u('blockquote', [
+        u('list', [
+          u('listItem', [
+            u('table', [
+              u('tableRow', [
+                u('tableCell', [
+                  u('heading', { depth: 1 }, [ u('text', 'Validly nested heading text.') ]),
+                ]),
+              ]),
+            ]),
+          ]),
+        ]),
+      ]),
+    ]);
+
+    const output = u('root', [
+      u('blockquote', [
+        u('list', [
+          u('listItem', [
+            u('table', [
+              u('tableRow', [
+                u('tableCell', [
+                  u('heading', { depth: 1 }, [ u('text', 'Validly nested heading text.') ]),
+                ]),
+              ]),
+            ]),
+          ]),
+        ]),
+      ]),
+    ]);
+
+    expect(transform(input)).toEqual(output);
+  });
+});
diff --git a/src/components/Widgets/Markdown/serializers/index.js b/src/components/Widgets/Markdown/serializers/index.js
index c66fc890..d7663450 100644
--- a/src/components/Widgets/Markdown/serializers/index.js
+++ b/src/components/Widgets/Markdown/serializers/index.js
@@ -9,6 +9,7 @@ import htmlToRehype from 'rehype-parse';
 import rehypeToRemark from 'rehype-remark';
 import remarkToRehypeShortcodes from './remarkRehypeShortcodes';
 import rehypePaperEmoji from './rehypePaperEmoji';
+import remarkAssertParents from './remarkAssertParents';
 import remarkWrapHtml from './remarkWrapHtml';
 import remarkToSlatePlugin from './remarkSlate';
 import remarkSquashReferences from './remarkSquashReferences';
@@ -199,10 +200,11 @@ export const htmlToSlate = html => {
 
   const mdast = unified()
     .use(rehypePaperEmoji)
-    .use(rehypeToRemark)
+    .use(rehypeToRemark, { minify: false })
     .runSync(hast);
 
   const slateRaw = unified()
+    .use(remarkAssertParents)
     .use(remarkImagesToText)
     .use(remarkShortcodes, { plugins: registry.getEditorComponents() })
     .use(remarkWrapHtml)
diff --git a/src/components/Widgets/Markdown/serializers/remarkAssertParents.js b/src/components/Widgets/Markdown/serializers/remarkAssertParents.js
new file mode 100644
index 00000000..afbc20b8
--- /dev/null
+++ b/src/components/Widgets/Markdown/serializers/remarkAssertParents.js
@@ -0,0 +1,83 @@
+import { concat, last, nth, isEmpty, set } from 'lodash';
+import visitParents from 'unist-util-visit-parents';
+
+/**
+ * remarkUnwrapInvalidNest
+ *
+ * Some MDAST node types can only be nested within specific node types - for
+ * example, a paragraph can't be nested within another paragraph, and a heading
+ * can't be nested in a "strong" type node. This kind of invalid MDAST can be
+ * generated by rehype-remark from invalid HTML.
+ *
+ * This plugin finds instances of invalid nesting, and unwraps the invalidly
+ * nested nodes as far up the parental line as necessary, splitting parent nodes
+ * along the way. The resulting node has no invalidly nested nodes, and all
+ * validly nested nodes retain their ancestry. Nodes that are emptied as a
+ * result of unnesting nodes are removed from the tree.
+ */
+export default function remarkUnwrapInvalidNest() {
+  return transform;
+
+  function transform(tree) {
+    const invalidNest = findInvalidNest(tree);
+
+    if (!invalidNest) return tree;
+
+    splitTreeAtNest(tree, invalidNest);
+
+    return transform(tree);
+  }
+
+  /**
+   * visitParents uses unist-util-visit-parent to check every node in the
+   * tree while having access to every ancestor of the node. This is ideal
+   * for determining whether a block node has an ancestor that should not
+   * contain a block node. Note that it operates in a mutable fashion.
+   */
+  function findInvalidNest(tree) {
+    /**
+     * Node types that are considered "blocks".
+     */
+    const blocks = ['paragraph', 'heading', 'code', 'blockquote', 'list', 'table', 'thematicBreak'];
+
+    /**
+     * Node types that can contain "block" nodes as direct children. We check
+     */
+    const canContainBlocks = ['root', 'blockquote', 'listItem', 'tableCell'];
+
+    let invalidNest;
+
+    visitParents(tree, (node, parents) => {
+      const parentType = !isEmpty(parents) && last(parents).type;
+      const isInvalidNest = blocks.includes(node.type) && !canContainBlocks.includes(parentType);
+
+      if (isInvalidNest) {
+        invalidNest = concat(parents, node);
+        return false;
+      }
+    });
+
+    return invalidNest;
+  }
+
+  function splitTreeAtNest(tree, nest) {
+    const grandparent = nth(nest, -3) || tree;
+    const parent = nth(nest, -2);
+    const node = last(nest);
+
+    const splitIndex = grandparent.children.indexOf(parent);
+    const splitChildren = grandparent.children;
+    const splitChildIndex = parent.children.indexOf(node);
+
+    const childrenBefore = parent.children.slice(0, splitChildIndex);
+    const childrenAfter = parent.children.slice(splitChildIndex + 1);
+    const nodeBefore = !isEmpty(childrenBefore) && { ...parent, children: childrenBefore };
+    const nodeAfter = !isEmpty(childrenAfter) && { ...parent, children: childrenAfter };
+
+    const childrenToInsert = [nodeBefore, node, nodeAfter].filter(val => !isEmpty(val));
+    const beforeChildren = splitChildren.slice(0, splitIndex);
+    const afterChildren = splitChildren.slice(splitIndex + 1);
+    const newChildren = concat(beforeChildren, childrenToInsert, afterChildren);
+    grandparent.children = newChildren;
+  }
+}
diff --git a/yarn.lock b/yarn.lock
index 97a6a911..2bdc0ff8 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -9036,6 +9036,10 @@ unist-util-stringify-position@^1.0.0:
   version "1.1.1"
   resolved "https://registry.yarnpkg.com/unist-util-stringify-position/-/unist-util-stringify-position-1.1.1.tgz#3ccbdc53679eed6ecf3777dd7f5e3229c1b6aa3c"
 
+unist-util-visit-parents@^1.1.1:
+  version "1.1.1"
+  resolved "https://registry.yarnpkg.com/unist-util-visit-parents/-/unist-util-visit-parents-1.1.1.tgz#7d3f56b5b039a3c6e2d16e51cc093f10e4755342"
+
 unist-util-visit@^1.0.0, unist-util-visit@^1.1.0, unist-util-visit@^1.1.1:
   version "1.1.3"
   resolved "https://registry.yarnpkg.com/unist-util-visit/-/unist-util-visit-1.1.3.tgz#ec268e731b9d277a79a5b5aa0643990e405d600b"