diff --git a/src/codecs/rotate/processor.ts b/src/codecs/rotate/processor.ts
index 0f795e51c..30bac75c4 100644
--- a/src/codecs/rotate/processor.ts
+++ b/src/codecs/rotate/processor.ts
@@ -11,7 +11,7 @@ export async function rotate(
 
   // Number of wasm memory pages (á 64KiB) needed to store the image twice.
   const bytesPerImage = data.width * data.height * 4;
-  const numPagesNeeded = Math.ceil(bytesPerImage * 2 / (64 * 1024) + 4);
+  const numPagesNeeded = Math.ceil((bytesPerImage * 2 + 4) / (64 * 1024));
   // Only count full pages, just to be safe.
   const numPagesAvailable = Math.floor(instance.exports.memory.buffer.byteLength / (64 * 1024));
   const additionalPagesToAllocate = numPagesNeeded - numPagesAvailable;
@@ -20,13 +20,13 @@ export async function rotate(
     instance.exports.memory.grow(additionalPagesToAllocate);
   }
   const view = new Uint8ClampedArray(instance.exports.memory.buffer);
-  view.set(data.data);
+  view.set(data.data, 4);
 
   instance.exports.rotate(data.width, data.height, opts.rotate);
 
   const flipDimensions = opts.rotate % 180 !== 0;
   return new ImageData(
-    view.slice(bytesPerImage, bytesPerImage * 2),
+    view.slice(bytesPerImage + 4, bytesPerImage * 2 + 4),
     flipDimensions ? data.height : data.width,
     flipDimensions ? data.width : data.height,
   );