diff --git a/crates/prek-identify/gen.py b/crates/prek-identify/gen.py
index ad70dc440..041cbcbe3 100644
--- a/crates/prek-identify/gen.py
+++ b/crates/prek-identify/gen.py
@@ -37,6 +37,14 @@
     ("TAG_SET_YAML", ["yaml"]),
 ]
 
+# This override is intentionally undesirable: it may diverge from upstream
+# identify, but upstream is unlikely to accept this mapping. We reluctantly
+# carry it here because there is no practical upstream path for now.
+EXTENSION_OVERRIDES = {
+    "cts": {"text", "ts"},
+    "mts": {"text", "ts"},
+}
+
 SELF_DIR = Path(__file__).parent
 TAGS_FILE = SELF_DIR / "src/tags.rs"
 
@@ -77,6 +85,7 @@ def tagset_expr(tag_set):
         f.write("};\n\n")
 
         EXTENSIONS.update(EXTENSIONS_NEED_BINARY_CHECK)
+        EXTENSIONS.update(EXTENSION_OVERRIDES)
         f.write("pub const EXTENSIONS: phf::Map<&str, TagSet> = phf::phf_map! {\n")
         for ext in sorted(EXTENSIONS):
             tag_names = sorted(EXTENSIONS[ext])
diff --git a/crates/prek-identify/src/lib.rs b/crates/prek-identify/src/lib.rs
index 73ab76750..e7b45385f 100644
--- a/crates/prek-identify/src/lib.rs
+++ b/crates/prek-identify/src/lib.rs
@@ -573,6 +573,12 @@ mod tests {
         let tags = super::tags_from_filename(Path::new("data.json"));
         assert_tagset(&tags, &["json", "text"]);
 
+        let tags = super::tags_from_filename(Path::new("index.cts"));
+        assert_tagset(&tags, &["text", "ts"]);
+
+        let tags = super::tags_from_filename(Path::new("index.mts"));
+        assert_tagset(&tags, &["text", "ts"]);
+
         let tags = super::tags_from_filename(Path::new("build.props"));
         assert_tagset(&tags, &["msbuild", "text", "xml"]);
 
diff --git a/crates/prek-identify/src/tags.rs b/crates/prek-identify/src/tags.rs
index f7dab13ba..c649446de 100644
--- a/crates/prek-identify/src/tags.rs
+++ b/crates/prek-identify/src/tags.rs
@@ -488,6 +488,8 @@ pub const EXTENSIONS: phf::Map<&str, TagSet> = phf::phf_map! {
     "csv" => TagSet::new(&[48, 255]),
     // ["c#", "c#script", "text"]
     "csx" => TagSet::new(&[29, 30, 255]),
+    // ["text", "ts"]
+    "cts" => TagSet::new(&[255, 261]),
     // ["cuda", "text"]
     "cu" => TagSet::new(&[49, 255]),
     // ["cue", "text"]
@@ -756,6 +758,8 @@ pub const EXTENSIONS: phf::Map<&str, TagSet> = phf::phf_map! {
     "mscx" => TagSet::new(&[169, 255, 297]),
     // ["binary", "musescore", "zip"]
     "mscz" => TagSet::new(&[21, 169, 308]),
+    // ["text", "ts"]
+    "mts" => TagSet::new(&[255, 261]),
     // ["mustache", "text"]
     "mustache" => TagSet::new(&[170, 255]),
     // ["myst", "text"]