diff --git a/src/main/kotlin/com/bolenpad/photophetch/ui/AppState.kt b/src/main/kotlin/com/bolenpad/photophetch/ui/AppState.kt
index b72cfcf..a6d062e 100644
--- a/src/main/kotlin/com/bolenpad/photophetch/ui/AppState.kt
+++ b/src/main/kotlin/com/bolenpad/photophetch/ui/AppState.kt
@@ -234,13 +234,19 @@ class AppState(private val configStore: ConfigStore) {
                     val tmpFile = tmpDir.resolve("$hash.$ext")
                     val cachePath = cacheDir.resolve("$hash.jpg")
                     if (tmpFile.toFile().exists() && tmpFile.toFile().length() > 0 && !cachePath.toFile().exists()) {
-                        val sips = ProcessBuilder("sips", "--resampleWidth", "240",
-                            tmpFile.toString(), "--out", cachePath.toString())
-                            .redirectErrorStream(true).start()
+                        // sips: resample to 240px wide AND convert to JPEG
+                        // --setProperty format jpeg ensures HEIC files are converted
+                        val sips = ProcessBuilder(
+                            "sips",
+                            "--resampleWidth", "240",
+                            "--setProperty", "format", "jpeg",
+                            tmpFile.toString(),
+                            "--out", cachePath.toString()
+                        ).redirectErrorStream(true).start()
                         sips.inputStream.readBytes()
                         sips.waitFor()
                         tmpFile.toFile().delete()
-                        if (cachePath.toFile().exists()) batchLoaded++
+                        if (cachePath.toFile().exists() && cachePath.toFile().length() > 0) batchLoaded++
                     }
                 }
                 loaded += batchLoaded
diff --git a/src/main/kotlin/com/bolenpad/photophetch/util/ThumbnailCache.kt b/src/main/kotlin/com/bolenpad/photophetch/util/ThumbnailCache.kt
index eb5e198..fd8b15f 100644
--- a/src/main/kotlin/com/bolenpad/photophetch/util/ThumbnailCache.kt
+++ b/src/main/kotlin/com/bolenpad/photophetch/util/ThumbnailCache.kt
@@ -56,10 +56,13 @@ object ThumbnailCache {
             val success = pullFn(devicePath, tmpFile)
             if (!success || !tmpFile.exists() || tmpFile.toFile().length() == 0L) return null
 
-            // Resize to thumbnail via sips (macOS built-in)
+            // Resize to thumbnail via sips — also converts HEIC→JPEG
             val sips = ProcessBuilder(
-                "sips", "--resampleWidth", "240",
-                tmpFile.toString(), "--out", cachePath.toString()
+                "sips",
+                "--resampleWidth", "240",
+                "--setProperty", "format", "jpeg",
+                tmpFile.toString(),
+                "--out", cachePath.toString()
             ).redirectErrorStream(true).start()
             sips.inputStream.readBytes()
             sips.waitFor()
diff --git a/src/main/resources/scripts/photophetch-ios-helper.py b/src/main/resources/scripts/photophetch-ios-helper.py
index 3c8a29c..ede570f 100644
--- a/src/main/resources/scripts/photophetch-ios-helper.py
+++ b/src/main/resources/scripts/photophetch-ios-helper.py
@@ -162,6 +162,9 @@ async def cmd_batch_thumbs(pairs_json: str):
     Pull thumbnails for multiple files in a single AFC session.
     Input: JSON array of [device_path, local_path] pairs.
     Output: JSON array of {devicePath, ok} results.
+    
+    For HEIC/HEIF files: pulls full file (partial read produces broken output).
+    For JPEG/PNG: reads first 512KB (enough for thumbnail extraction).
     """
     try:
         pairs = json.loads(pairs_json)
@@ -169,16 +172,21 @@ async def cmd_batch_thumbs(pairs_json: str):
         afc = await get_afc(lockdown)
         results = []
         for device_path, local_path in pairs:
+            ext = device_path.rsplit('.', 1)[-1].lower() if '.' in device_path else ''
+            is_heic = ext in ('heic', 'heif')
             try:
                 os.makedirs(os.path.dirname(os.path.abspath(local_path)), exist_ok=True)
-                try:
-                    data = await afc.fread(device_path, 512 * 1024, 0)
-                except Exception:
+                if is_heic:
+                    # HEIC: must pull full file — partial reads produce broken output
                     await afc.pull(device_path, local_path)
-                    results.append({'devicePath': device_path, 'ok': True})
-                    continue
-                with open(local_path, 'wb') as f:
-                    f.write(data)
+                else:
+                    # JPEG/PNG: 512KB partial read is sufficient
+                    try:
+                        data = await afc.fread(device_path, 512 * 1024, 0)
+                        with open(local_path, 'wb') as f:
+                            f.write(data)
+                    except Exception:
+                        await afc.pull(device_path, local_path)
                 results.append({'devicePath': device_path, 'ok': True})
             except Exception as e:
                 results.append({'devicePath': device_path, 'ok': False, 'error': str(e)})