diff --git a/src/Rules/PreRule.php b/src/Rules/PreRule.php
index 15b3113..7c8cc8d 100644
--- a/src/Rules/PreRule.php
+++ b/src/Rules/PreRule.php
@@ -10,16 +10,18 @@
 
 final class PreRule implements Rule, ProvidesFirstChar
 {
-    public string $firstChar = '`';
+    public string $firstChar = '`~';
 
     public function shouldParse(Parser $parser): bool
     {
-        return $parser->comesNext('```', 3);
+        return $parser->comesNext('```', 3) || $parser->comesNext('~~~', 3);
     }
 
     public function parse(Parser $parser): Token
     {
-        $parser->consumeIncluding('```');
+        // A fence is a run of at least three backticks or tildes, and is
+        // closed by a run of the same character.
+        $fence = $parser->consumeWhile($parser->current ?? '`');
 
         $language = $parser->consumeUntil(Parser::WHITESPACE);
 
@@ -27,9 +29,9 @@ public function parse(Parser $parser): Token
 
         $parser->consumeWhile(Parser::NEW_LINE);
 
-        $content = $parser->consumeUntilString('```');
+        $content = $parser->consumeUntilString($fence);
 
-        $parser->consumeIncluding('```');
+        $parser->consumeIncluding($fence);
         $parser->consumeWhile(Parser::NEW_LINE);
 
         // Remove trailing newline.
diff --git a/tests/Rules/PreRuleTest.php b/tests/Rules/PreRuleTest.php
index d3c036d..0e613cf 100644
--- a/tests/Rules/PreRuleTest.php
+++ b/tests/Rules/PreRuleTest.php
@@ -5,6 +5,8 @@
 use PHPUnit\Framework\Attributes\Test;
 use Tempest\Markdown\Parser;
 use Tempest\Markdown\Rules\PreRule;
+use Tempest\Markdown\Rules\StrikethroughRule;
+use Tempest\Markdown\Rules\TextRule;
 use Tempest\Markdown\Tests\ParserTestCase;
 
 class PreRuleTest extends ParserTestCase
@@ -88,4 +90,54 @@ public function test_lex_with_backtick_in_content(): void
             $html,
         );
     }
+
+    #[Test]
+    public function lex_tilde_fence(): void
+    {
+        $html =
+            (string) new Parser(highlighter: null, rules: [new PreRule()])->parse(
+                "~~~\ncode\n~~~",
+            );
+
+        $this->assertSame('<pre>code</pre>', $html);
+    }
+
+    #[Test]
+    public function lex_tilde_fence_with_language(): void
+    {
+        $html =
+            (string) new Parser(highlighter: null, rules: [new PreRule()])->parse(
+                "~~~php\n\$a = 1;\n~~~",
+            );
+
+        $this->assertSame('<pre class="language-php">$a = 1;</pre>', $html);
+    }
+
+    #[Test]
+    public function lex_longer_fence_may_contain_a_shorter_one(): void
+    {
+        $parser = new Parser(highlighter: null, rules: [new PreRule()]);
+
+        $this->assertSame(
+            '<pre>a ``` b</pre>',
+            (string) $parser->parse("````\na ``` b\n````"),
+        );
+
+        $this->assertSame(
+            '<pre>a ~~~ b</pre>',
+            (string) $parser->parse("~~~~\na ~~~ b\n~~~~"),
+        );
+    }
+
+    #[Test]
+    public function lex_does_not_take_over_strikethrough(): void
+    {
+        $html = (string) new Parser(highlighter: null, rules: [
+            new PreRule(),
+            new StrikethroughRule(),
+            new TextRule(),
+        ])->parse('a ~~b~~ c');
+
+        $this->assertSame('a <s>b</s> c', $html);
+    }
 }