diff --git a/tools/chatgui/ffmpeg/build_ffmpeg.sh b/tools/chatgui/ffmpeg/build_ffmpeg.sh
index c88bff21..bc2d1399 100755
--- a/tools/chatgui/ffmpeg/build_ffmpeg.sh
+++ b/tools/chatgui/ffmpeg/build_ffmpeg.sh
@@ -93,6 +93,12 @@ fi
 # --- x265 (H.265/HEVC encoder) ---
 if [ ! -f "$INSTALL_DIR/lib/pkgconfig/x265.pc" ]; then
     do_clone x265 https://bitbucket.org/multicoreware/x265_git.git master
+    if [ -f "$SRC_DIR/x265/.git/shallow" ]; then
+        log "Fetch x265 history and release tags..."
+        git -C "$SRC_DIR/x265" fetch --unshallow --tags origin
+    fi
+    X265_TAG=$(git -C "$SRC_DIR/x265" describe --abbrev=0 --tags 2>/dev/null || true)
+    [ -n "$X265_TAG" ] || die "Cannot determine x265 release tag; check the x265 Git remote and tags"
     cd "$SRC_DIR/x265"
     mkdir -p build && cd build
     log "Configure x265..."