Slack won't accept my HEIC
Slack supports HEIC inconsistently. The web client and Mac app usually accept it; the Android app and some Windows desktop builds reject it with 'unsupported file type.' The reliable workaround is to convert the HEIC to JPG before uploading.
The fix
Convert your HEIC to JPG using the converter on this site. Drop the file, click Convert, upload the JPG to Slack instead. Conversion runs in your browser — no upload, no signup.
Why this happens with Slack specifically
- Slack uses different image libraries on different platforms
- The Android client in particular has never had reliable HEIC decoding
- Even when Slack accepts the upload, the resulting preview may look broken to teammates on Windows clients
- Slack's own engineering team has acknowledged HEIC is not a first-class supported format
The long-term workaround
If you frequently share iPhone photos in Slack, the cleanest long-term fix is to switch your iPhone Camera setting to Most Compatible (Settings → Camera → Formats → Most Compatible). New photos will save as JPG and Slack will accept them directly. See the full tutorial.