diff --git a/shader/fine.wgsl b/shader/fine.wgsl
index 5f90f6e..a30b0de 100644
--- a/shader/fine.wgsl
+++ b/shader/fine.wgsl
@@ -33,7 +33,15 @@
 var<storage> info: array<u32>;
 
 @group(0) @binding(4)
+#ifdef r8
+// The R8 variant is available via a non-standard extension in Dawn. We can't
+// optionally declare that extension here since naga doesn't understand the
+// `enable` directive (see https://github.com/gfx-rs/wgpu/issues/5476). The
+// directive must be injected by the client via some other means.
+var output: texture_storage_2d<r8unorm, write>;
+#else
 var output: texture_storage_2d<rgba8unorm, write>;
+#endif
 
 #ifdef full
 @group(0) @binding(5)
diff --git a/shader/permutations b/shader/permutations
index b235168..011541e 100644
--- a/shader/permutations
+++ b/shader/permutations
@@ -5,3 +5,6 @@
 + fine_area
 + fine_msaa8: msaa msaa8
 + fine_msaa16: msaa msaa16
++ fine_area_r8: r8
++ fine_msaa8_r8: msaa msaa8 r8
++ fine_msaa16_r8: msaa msaa16 r8