diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 42bb163..bb8727d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -33,10 +33,18 @@ jobs:
       - name: Install the tools the fixtures are built with
         run: |
           sudo apt-get update
-          sudo apt-get install -y ffmpeg libimage-exiftool-perl libheif-examples
+          sudo apt-get install -y ffmpeg libimage-exiftool-perl \
+            libheif-examples libheif-plugin-x265
           for tool in ffmpeg exiftool heif-enc; do
             command -v "$tool" || { echo "::error::$tool did not resolve"; exit 1; }
           done
+          # Resolving heif-enc is not the same claim as being able to encode:
+          # Ubuntu splits the HEVC encoder into its own plugin, so the binary
+          # is there and answers "No HEVC encoder available". One real encode
+          # fails here, naming the problem, instead of inside a fixture builder.
+          ffmpeg -loglevel error -f lavfi -i color=c=red:s=32x32 -frames:v 1 -y /tmp/probe.png
+          heif-enc -q 50 /tmp/probe.png -o /tmp/probe.heic
+          test -s /tmp/probe.heic || { echo "::error::heif-enc produced nothing"; exit 1; }
 
       - name: Install uv
         uses: astral-sh/setup-uv@v5