diff --git a/codex-rs/tui/src/diff_render.rs b/codex-rs/tui/src/diff_render.rs
index 58410baf33..388d282bc9 100644
--- a/codex-rs/tui/src/diff_render.rs
+++ b/codex-rs/tui/src/diff_render.rs
@@ -2222,34 +2222,37 @@ mod tests {
 
     #[test]
     fn cpp_module_extensions_use_cpp_highlighting() {
-        let highlighted_tokens = ["cpp", "cppm", "CPPM", "cxxm", "CxXm", "ixx", "IXX"]
-            .into_iter()
-            .map(|extension| {
-                let mut changes: HashMap<PathBuf, FileChange> = HashMap::new();
-                changes.insert(
-                    PathBuf::from(format!("math.{extension}")),
-                    FileChange::Add {
-                        content:
-                            "export module math;\nexport int sum(int a, int b) { return a + b; }\n"
-                                .to_string(),
-                    },
-                );
+        let highlighted_tokens = [
+            "cpp",
+            // CUDA source and header extensions use C++ highlighting as a fallback.
+            "cu", "cuh", "cppm", "CPPM", "cxxm", "CxXm", "ixx", "IXX",
+        ]
+        .into_iter()
+        .map(|extension| {
+            let mut changes: HashMap<PathBuf, FileChange> = HashMap::new();
+            changes.insert(
+                PathBuf::from(format!("math.{extension}")),
+                FileChange::Add {
+                    content:
+                        "export module math;\nexport int sum(int a, int b) { return a + b; }\n"
+                            .to_string(),
+                },
+            );
 
-                let lines =
-                    create_diff_summary(&changes, &PathBuf::from("/"), /*wrap_cols*/ 80);
-                let rgb_tokens = lines
-                    .iter()
-                    .flat_map(|line| &line.spans)
-                    .filter(|span| matches!(span.style.fg, Some(ratatui::style::Color::Rgb(..))))
-                    .map(|span| span.content.to_string())
-                    .collect::<Vec<_>>();
-                assert!(
-                    !rgb_tokens.is_empty(),
-                    "add diff for .{extension} file should produce syntax-highlighted (RGB) spans"
-                );
-                (extension, rgb_tokens.join("|"))
-            })
-            .collect::<Vec<_>>();
+            let lines = create_diff_summary(&changes, &PathBuf::from("/"), /*wrap_cols*/ 80);
+            let rgb_tokens = lines
+                .iter()
+                .flat_map(|line| &line.spans)
+                .filter(|span| matches!(span.style.fg, Some(ratatui::style::Color::Rgb(..))))
+                .map(|span| span.content.to_string())
+                .collect::<Vec<_>>();
+            assert!(
+                !rgb_tokens.is_empty(),
+                "add diff for .{extension} file should produce syntax-highlighted (RGB) spans"
+            );
+            (extension, rgb_tokens.join("|"))
+        })
+        .collect::<Vec<_>>();
 
         assert_debug_snapshot!("cpp_module_extension_highlighting", highlighted_tokens);
     }
diff --git a/codex-rs/tui/src/render/highlight.rs b/codex-rs/tui/src/render/highlight.rs
index f0b77f6652..058dbc8a45 100644
--- a/codex-rs/tui/src/render/highlight.rs
+++ b/codex-rs/tui/src/render/highlight.rs
@@ -539,6 +539,8 @@ fn find_syntax(lang: &str) -> Option<&'static SyntaxReference> {
     let normalized = lang.to_ascii_lowercase();
     let patched = match normalized.as_str() {
         "csharp" | "c-sharp" => "c#",
+        // CUDA source (.cu) and header (.cuh) files use C++ highlighting as a fallback.
+        "cu" | "cuh" => "cpp",
         "cppm" | "cxxm" | "ixx" => "cpp",
         "golang" => "go",
         "python3" => "python",
@@ -1216,8 +1218,8 @@ mod tests {
         }
         // Patched aliases that two-face cannot resolve on its own.
         for alias in [
-            "csharp", "c-sharp", "cppm", "CPPM", "cxxm", "CxXm", "ixx", "IXX", "golang", "python3",
-            "shell",
+            "csharp", "c-sharp", "cu", "cuh", "cppm", "CPPM", "cxxm", "CxXm", "ixx", "IXX",
+            "golang", "python3", "shell",
         ] {
             assert!(
                 find_syntax(alias).is_some(),
diff --git a/codex-rs/tui/src/snapshots/codex_tui__diff_render__tests__cpp_module_extension_highlighting.snap b/codex-rs/tui/src/snapshots/codex_tui__diff_render__tests__cpp_module_extension_highlighting.snap
index be5ab4fe17..3376f8f04c 100644
--- a/codex-rs/tui/src/snapshots/codex_tui__diff_render__tests__cpp_module_extension_highlighting.snap
+++ b/codex-rs/tui/src/snapshots/codex_tui__diff_render__tests__cpp_module_extension_highlighting.snap
@@ -7,6 +7,14 @@ expression: highlighted_tokens
         "cpp",
         "export| module math|;|export| |int| |sum|(|int| |a|,| |int| |b|)| |{| |return| a |+| b|;| |}",
     ),
+    (
+        "cu",
+        "export| module math|;|export| |int| |sum|(|int| |a|,| |int| |b|)| |{| |return| a |+| b|;| |}",
+    ),
+    (
+        "cuh",
+        "export| module math|;|export| |int| |sum|(|int| |a|,| |int| |b|)| |{| |return| a |+| b|;| |}",
+    ),
     (
         "cppm",
         "export| module math|;|export| |int| |sum|(|int| |a|,| |int| |b|)| |{| |return| a |+| b|;| |}",