diff --git a/news/changelog-1.9.md b/news/changelog-1.9.md
index 1d9fe8db3ba..3061fc3e0c2 100644
--- a/news/changelog-1.9.md
+++ b/news/changelog-1.9.md
@@ -163,3 +163,4 @@ All changes included in 1.9:
 - ([#13890](https://github.com/quarto-dev/quarto-cli/issues/13890)): Fix render failure when using `embed-resources: true` with input path through a symlinked directory. The cleanup now resolves symlinks before comparing paths.
 - ([#13907](https://github.com/quarto-dev/quarto-cli/issues/13907)): Ignore AI assistant configuration files (`CLAUDE.md`, `AGENTS.md`) when scanning for project input files and in extension templates, similar to how `README.md` is handled.
 - ([#13935](https://github.com/quarto-dev/quarto-cli/issues/13935)): Fix `quarto install`, `quarto update`, and `quarto uninstall` interactive tool selection.
+- ([#13998](https://github.com/quarto-dev/quarto-cli/issues/13998)): Fix YAML validation error with CR-only line terminators (old Mac format). Documents using `\r` line endings no longer fail with "Expected YAML front matter to contain at least 2 lines".
diff --git a/src/core/lib/ranged-text.ts b/src/core/lib/ranged-text.ts
index d9c93849707..e84e9912e22 100644
--- a/src/core/lib/ranged-text.ts
+++ b/src/core/lib/ranged-text.ts
@@ -40,7 +40,7 @@ export function rangedLines(
   text: string,
   includeNewLines = false,
 ): RangedSubstring[] {
-  const regex = /\r?\n/g;
+  const regex = /\r\n?|\n/g;
   const result: RangedSubstring[] = [];
 
   let startOffset = 0;
diff --git a/src/core/lib/text.ts b/src/core/lib/text.ts
index 7bdeda461aa..eec3f931633 100644
--- a/src/core/lib/text.ts
+++ b/src/core/lib/text.ts
@@ -9,7 +9,7 @@ import { InternalError } from "./error.ts";
 import { quotedStringColor } from "./errors.ts";
 
 export function lines(text: string): string[] {
-  return text.split(/\r?\n/);
+  return text.split(/\r\n?|\n/);
 }
 
 export function normalizeNewlines(text: string) {
@@ -62,13 +62,13 @@ export function* matchAll(text: string, regexp: RegExp) {
 
 export function* lineOffsets(text: string) {
   yield 0;
-  for (const match of matchAll(text, /\r?\n/g)) {
+  for (const match of matchAll(text, /\r\n?|\n/g)) {
     yield match.index + match[0].length;
   }
 }
 
 export function* lineBreakPositions(text: string) {
-  for (const match of matchAll(text, /\r?\n/g)) {
+  for (const match of matchAll(text, /\r\n?|\n/g)) {
     yield match.index;
   }
 }
diff --git a/tests/smoke/yaml/yaml-cr-line-endings.test.ts b/tests/smoke/yaml/yaml-cr-line-endings.test.ts
new file mode 100644
index 00000000000..43ea27c4638
--- /dev/null
+++ b/tests/smoke/yaml/yaml-cr-line-endings.test.ts
@@ -0,0 +1,24 @@
+/*
+* yaml-cr-line-endings.test.ts
+*
+* Test YAML validation with CR-only line endings (old Mac format)
+* See: https://github.com/quarto-dev/quarto-cli/issues/13998
+*
+* Copyright (C) 2025 Posit Software, PBC
+*/
+
+import { testRender } from "../render/render.ts";
+import { noErrorsOrWarnings } from "../../verify.ts";
+import { join } from "../../../src/deno_ral/path.ts";
+
+// Create test file with CR-only line endings programmatically
+const dir = Deno.makeTempDirSync({ prefix: "quarto-cr-test-" });
+const crContent = "---\rtitle: \"CR Test\"\rauthor: \"Test Author\"\r---\r\rContent here.\r";
+const inputFile = join(dir, "cr-only.qmd");
+Deno.writeFileSync(inputFile, new TextEncoder().encode(crContent));
+
+testRender(inputFile, "html", false, [noErrorsOrWarnings], {
+  teardown: async () => {
+    Deno.removeSync(dir, { recursive: true });
+  },
+});
diff --git a/tests/unit/core/lib/text.test.ts b/tests/unit/core/lib/text.test.ts
index a75eeeb2b97..792a95c8874 100644
--- a/tests/unit/core/lib/text.test.ts
+++ b/tests/unit/core/lib/text.test.ts
@@ -6,7 +6,7 @@
 
 import { unitTest } from "../../../test.ts";
 import { assertEquals } from "testing/asserts";
-import { getEndingNewlineCount } from "../../../../src/core/lib/text.ts";
+import { getEndingNewlineCount, lines } from "../../../../src/core/lib/text.ts";
 
 unitTest("core/lib/text.ts - getEndingNewlineCount", async () => {
   // Test case 1: No trailing newlines
@@ -64,3 +64,34 @@ unitTest("core/lib/text.ts - getEndingNewlineCount", async () => {
     3,
   );
 });
+
+// Test for lines() function with different line endings
+// See: https://github.com/quarto-dev/quarto-cli/issues/13998
+unitTest("core/lib/text.ts - lines() with different line endings", async () => {
+  // LF (Unix/Linux)
+  assertEquals(lines("a\nb\nc"), ["a", "b", "c"]);
+
+  // CRLF (Windows)
+  assertEquals(lines("a\r\nb\r\nc"), ["a", "b", "c"]);
+
+  // CR-only (old Mac) - the fix for #13998
+  assertEquals(lines("a\rb\rc"), ["a", "b", "c"]);
+
+  // Mixed endings
+  assertEquals(lines("a\rb\nc\r\nd"), ["a", "b", "c", "d"]);
+
+  // YAML front matter with CR-only
+  const yaml = "---\rtitle: \"Test\"\r---";
+  assertEquals(lines(yaml), ["---", "title: \"Test\"", "---"]);
+
+  // Empty string
+  assertEquals(lines(""), [""]);
+
+  // Single line without newline
+  assertEquals(lines("single"), ["single"]);
+
+  // Trailing newlines
+  assertEquals(lines("a\n"), ["a", ""]);
+  assertEquals(lines("a\r"), ["a", ""]);
+  assertEquals(lines("a\r\n"), ["a", ""]);
+});