diff --git a/Cargo.lock b/Cargo.lock
index bb8ef2fba3b17..dcf953a4f0724 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3259,6 +3259,7 @@ version = "0.0.0"
 dependencies = [
  "insta",
  "regex",
+ "ruff_linter",
  "ruff_python_ast",
  "ruff_python_formatter",
  "ruff_python_trivia",
diff --git a/crates/ruff_linter/src/settings/types.rs b/crates/ruff_linter/src/settings/types.rs
index c81e21d64c53a..ce22da37b1319 100644
--- a/crates/ruff_linter/src/settings/types.rs
+++ b/crates/ruff_linter/src/settings/types.rs
@@ -500,6 +500,11 @@ impl ExtensionMapping {
         let ext = path.extension()?.to_str()?;
         self.0.get(ext).copied()
     }
+
+    /// Return the [`Language`] for a given file extension.
+    pub fn get_extension(&self, ext: &str) -> Option<Language> {
+        self.0.get(ext).copied()
+    }
 }
 
 impl From<FxHashMap<String, Language>> for ExtensionMapping {
diff --git a/crates/ruff_markdown/Cargo.toml b/crates/ruff_markdown/Cargo.toml
index c611deeecd0f4..f40d1e3b8cacb 100644
--- a/crates/ruff_markdown/Cargo.toml
+++ b/crates/ruff_markdown/Cargo.toml
@@ -17,8 +17,12 @@ ruff_source_file = { workspace = true }
 ruff_text_size = { workspace = true }
 ruff_workspace = { workspace = true }
 
-insta = { workspace = true }
 regex = { workspace = true }
 
+[dev-dependencies]
+ruff_linter = { workspace = true }
+
+insta = { workspace = true }
+
 [lints]
 workspace = true
diff --git a/crates/ruff_markdown/src/lib.rs b/crates/ruff_markdown/src/lib.rs
index 7277f0c7bf63e..a0cc4daf9a209 100644
--- a/crates/ruff_markdown/src/lib.rs
+++ b/crates/ruff_markdown/src/lib.rs
@@ -93,7 +93,10 @@ pub fn format_code_blocks(
                         let end = code_line.start();
                         let unformatted_code = dedent(&source[TextRange::new(start, end)]);
 
-                        let py_source_type = PySourceType::from_extension(&language);
+                        let py_source_type = match settings.extension.get_extension(&language) {
+                            None => PySourceType::from_extension(&language),
+                            Some(language) => PySourceType::from(language),
+                        };
                         let options =
                             settings.to_format_options(py_source_type, &unformatted_code, path);
 
@@ -132,6 +135,7 @@ pub fn format_code_blocks(
 #[cfg(test)]
 mod tests {
     use insta::assert_snapshot;
+    use ruff_linter::settings::types::{ExtensionMapping, ExtensionPair, Language};
     use ruff_workspace::FormatterSettings;
 
     use crate::{MarkdownResult, format_code_blocks};
@@ -384,4 +388,27 @@ print( 'hello' )
             &FormatterSettings::default()
         ), @"Unchanged");
     }
+
+    #[test]
+    fn format_code_blocks_extension_mapping() {
+        // format "py" mapped as "pyi" instead
+        let code = r#"
+```py
+def foo(): ...
+def bar(): ...
+```
+        "#;
+        let mapping = ExtensionMapping::from_iter([ExtensionPair {
+            extension: "py".to_string(),
+            language: Language::Pyi,
+        }]);
+        assert_snapshot!(format_code_blocks(
+            code,
+            None,
+            &FormatterSettings {
+                extension: mapping,
+                ..Default::default()
+            }
+        ), @"Unchanged");
+    }
 }