diff --git a/client/speed.js b/client/speed.js
index 70c5098..bd97e8c 100644
--- a/client/speed.js
+++ b/client/speed.js
@@ -138,7 +138,7 @@ function wasm_ensure_by(state, nstrokes, ncoords) {
   
         buffers['xs'].tv = tv_create_on(Float32Array, coords_bytes / 4, mem, buffers['xs'].offset);
         buffers['ys'].tv = tv_create_on(Float32Array, coords_bytes / 4, mem, buffers['ys'].offset);
-        buffers['pressures'].tv = tv_create_on(Uint8Array, coords_bytes / 8, mem, buffers['pressures'].offset);
+        buffers['pressures'].tv = tv_create_on(Uint8Array, coords_bytes, mem, buffers['pressures'].offset);
         buffers['coords_from'].tv = tv_create_on(Uint32Array, stroke_bytes / 4, mem, buffers['coords_from'].offset);
 
         // TODO: this should have been automatic maybe?