diff --git a/.changeset/plain-ads-build.md b/.changeset/plain-ads-build.md
new file mode 100644
index 0000000..217c275
--- /dev/null
+++ b/.changeset/plain-ads-build.md
@@ -0,0 +1,5 @@
+---
+'@sillsdev/lynx-delta': patch
+---
+
+Fix crash when adding a paragraph to the end of a ScriptureDeltaDocument
diff --git a/packages/delta/src/scripture-delta-document.test.ts b/packages/delta/src/scripture-delta-document.test.ts
index 8e080f1..04d0fd0 100644
--- a/packages/delta/src/scripture-delta-document.test.ts
+++ b/packages/delta/src/scripture-delta-document.test.ts
@@ -400,4 +400,40 @@ describe('ScriptureDeltaDocument', () => {
     expect(paragraph1.getText()).toEqual(`\ufffcVerse one.\ufffcVerse two.\n`);
     expect(paragraph1.range).toEqual({ start: { line: 1, character: 0 }, end: { line: 2, character: 0 } });
   });
+
+  it('add paragraph at end of document', () => {
+    const document = new ScriptureDeltaDocument(
+      'uri',
+      'scr-delta',
+      1,
+      new Delta()
+        .insert({ chapter: { number: '1', style: 'c' } })
+        .insert({ verse: { number: '1', style: 'v' } })
+        .insert('This is a test.', { segment: 'verse_1_1' })
+        .insert('\n', { para: { style: 'p' } })
+        .insert({ verse: { number: '2', style: 'v' } })
+        .insert('This is a test.', { segment: 'verse_1_2' })
+        .insert('\n', { para: { style: 'p' } }),
+    );
+
+    expect(document.children.length).toEqual(3);
+
+    document.update(
+      new Delta()
+        .retain(35)
+        .insert('section header.', { segment: 's_1' })
+        .insert('\n', { para: { style: 's' } }),
+      2,
+    );
+
+    expect(document.children.length).toEqual(4);
+
+    const paragraph2 = document.children[2];
+    expect(paragraph2.getText()).toEqual(`\ufffcThis is a test.\n`);
+    expect(paragraph2.range).toEqual({ start: { line: 2, character: 0 }, end: { line: 3, character: 0 } });
+
+    const paragraph3 = document.children[3];
+    expect(paragraph3.getText()).toEqual(`section header.\n`);
+    expect(paragraph3.range).toEqual({ start: { line: 3, character: 0 }, end: { line: 4, character: 0 } });
+  });
 });
diff --git a/packages/delta/src/scripture-delta-document.ts b/packages/delta/src/scripture-delta-document.ts
index e40c042..326f8b4 100644
--- a/packages/delta/src/scripture-delta-document.ts
+++ b/packages/delta/src/scripture-delta-document.ts
@@ -47,9 +47,14 @@ export class ScriptureDeltaDocument extends ScriptureDocumentMixin(DeltaDocument
     let lineChildren = this.lineChildren!;
     const childStartIndex = lineChildren[changeStartLine];
     const childEndIndex = lineChildren[changeEndLine];
-    const childStart = this.children[childStartIndex];
-    const childStartLine = childStart.range.start.line;
-    // const childEndLine = this.children[childEndIndex].range.end.line;
+    const childStartLine =
+      childStartIndex < this.children.length
+        ? this.children[childStartIndex].range.start.line
+        : lineChildren.length - 1;
+    const childStartPosition =
+      childStartIndex < this.children.length
+        ? this.children[childStartIndex].range.start
+        : this.children[this.children.length - 1].range.end;
     const childEndLine =
       childEndIndex < this.children.length ? this.children[childEndIndex].range.end.line : lineChildren.length - 1;
 
@@ -69,8 +74,8 @@ export class ScriptureDeltaDocument extends ScriptureDocumentMixin(DeltaDocument
       addedLineOffsets,
       addedLineChildren,
       addedLineOps,
-      childStart.range.start,
-      this.offsetAt(childStart.range.start),
+      childStartPosition,
+      this.offsetAt(childStartPosition),
       childStartIndex,
       opStartIndex,
     );