diff --git a/_11ty/img-dim.js b/_11ty/img-dim.js
index c3312b5..ca49ca7 100644
--- a/_11ty/img-dim.js
+++ b/_11ty/img-dim.js
@@ -59,10 +59,14 @@ const processImage = async (img, outputPath) => {
     img.setAttribute("width", dimensions.width);
     img.setAttribute("height", dimensions.height);
   }
-  const inputType = dimensions.type;
+  const inputType = (dimensions.type || "").toLowerCase();
   if (inputType == "svg") {
     return;
   }
+  if (inputType == "heif" || inputType == "heic") {
+    console.warn(`Skipping unsupported image type "${inputType}"`, src);
+    return;
+  }
   if (inputType == "gif") {
     const videoSrc = await gif2mp4(src);
     const video = img.ownerDocument.createElement(