diff --git a/src/back/hlsl/writer.rs b/src/back/hlsl/writer.rs
index 9b729282c4..c56164f751 100644
--- a/src/back/hlsl/writer.rs
+++ b/src/back/hlsl/writer.rs
@@ -2814,7 +2814,7 @@ impl<'a, W: fmt::Write> super::Writer<'a, W> {
                         Ctrl::Fine => "ddy_fine",
                         Ctrl::None => "ddy",
                     },
-                    _ => "fwidth",
+                    Axis::Width => "fwidth",
                 };
                 write!(self.out, "{fun_str}(")?;
                 self.write_expr(module, expr, func_ctx)?;