diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0cd4090..40fce02 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,11 @@
 - `nvim_oxi::api::KeymapInfos::buffer` is now an `Option<Buffer>` instead of
   a `bool` ([#255](https://github.com/noib3/nvim-oxi/pull/255));
 
+- `nvim_oxi::api::Buffer::get_extmarks()` now takes an
+  `impl Into<GetExtmarksNamespaceId>` as its first argument instead of a `u32`.
+  Because `GetExtmarksNamespaceId` implements `From<u32>`, this should be an
+  API-compatible change ([#256](https://github.com/noib3/nvim-oxi/pull/256));
+
 ### Fixed
 
 - fixed the definition of `DecorationProviderOpts`, which was causing
diff --git a/crates/api/src/extmark.rs b/crates/api/src/extmark.rs
index a818114..6415b2a 100644
--- a/crates/api/src/extmark.rs
+++ b/crates/api/src/extmark.rs
@@ -195,20 +195,20 @@ impl Buffer {
     /// was set to `true`.
     ///
     /// [1]: https://neovim.io/doc/user/api.html#nvim_buf_get_extmarks()
-    pub fn get_extmarks(
+    pub fn get_extmarks<NsId: Into<GetExtmarksNamespaceId>>(
         &self,
-        ns_id: u32,
+        ns_id: NsId,
         start: ExtmarkPosition,
         end: ExtmarkPosition,
         opts: &GetExtmarksOpts,
     ) -> Result<
-        impl SuperIterator<(u32, usize, usize, Option<ExtmarkInfos>)> + use<>,
+        impl SuperIterator<(u32, usize, usize, Option<ExtmarkInfos>)> + use<NsId>,
     > {
         let mut err = nvim::Error::new();
         let extmarks = unsafe {
             nvim_buf_get_extmarks(
                 self.0,
-                ns_id as Integer,
+                ns_id.into().into(),
                 start.into(),
                 end.into(),
                 opts,
diff --git a/crates/api/src/types/get_extmarks_namespace_id.rs b/crates/api/src/types/get_extmarks_namespace_id.rs
new file mode 100644
index 0000000..4b73e5f
--- /dev/null
+++ b/crates/api/src/types/get_extmarks_namespace_id.rs
@@ -0,0 +1,27 @@
+/// Namespace selector given to
+/// [`Buffer::get_extmarks`](crate::Buffer::get_extmarks).
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub enum GetExtmarksNamespaceId {
+    /// Get extmarks from all namespaces.
+    All,
+
+    /// Only get extmarks registered on the namespace with this ID.
+    Specific(u32),
+}
+
+impl From<u32> for GetExtmarksNamespaceId {
+    #[inline]
+    fn from(namespace_id: u32) -> Self {
+        Self::Specific(namespace_id)
+    }
+}
+
+impl From<GetExtmarksNamespaceId> for types::Integer {
+    #[inline]
+    fn from(namespace_id: GetExtmarksNamespaceId) -> Self {
+        match namespace_id {
+            GetExtmarksNamespaceId::All => -1,
+            GetExtmarksNamespaceId::Specific(id) => id as Self,
+        }
+    }
+}
diff --git a/crates/api/src/types/mod.rs b/crates/api/src/types/mod.rs
index 66ddd92..c4375b6 100644
--- a/crates/api/src/types/mod.rs
+++ b/crates/api/src/types/mod.rs
@@ -21,6 +21,7 @@ mod extmark_infos;
 mod extmark_position;
 mod extmark_virt_text_chunk;
 mod extmark_virt_text_position;
+mod get_extmarks_namespace_id;
 mod get_hl_infos;
 mod got_mode;
 mod highlight_infos;
@@ -73,6 +74,7 @@ pub use extmark_infos::*;
 pub use extmark_position::*;
 pub use extmark_virt_text_chunk::*;
 pub use extmark_virt_text_position::*;
+pub use get_extmarks_namespace_id::GetExtmarksNamespaceId;
 pub use get_hl_infos::GetHlInfos;
 pub use got_mode::*;
 pub use highlight_infos::*;