diff --git a/Tests/images/timeout-9139147ce93e20eb14088fe238e541443ffd64b3.fli b/Tests/images/timeout-9139147ce93e20eb14088fe238e541443ffd64b3.fli
index ce4607d2d..a7a3bd546 100644
Binary files a/Tests/images/timeout-9139147ce93e20eb14088fe238e541443ffd64b3.fli and b/Tests/images/timeout-9139147ce93e20eb14088fe238e541443ffd64b3.fli differ
diff --git a/Tests/images/timeout-bff0a9dc7243a8e6ede2408d2ffa6a9964698b87.fli b/Tests/images/timeout-bff0a9dc7243a8e6ede2408d2ffa6a9964698b87.fli
index 77a94b87a..4bc18b06a 100644
Binary files a/Tests/images/timeout-bff0a9dc7243a8e6ede2408d2ffa6a9964698b87.fli and b/Tests/images/timeout-bff0a9dc7243a8e6ede2408d2ffa6a9964698b87.fli differ
diff --git a/src/PIL/FliImagePlugin.py b/src/PIL/FliImagePlugin.py
index 7c5bfeefa..727a1316d 100644
--- a/src/PIL/FliImagePlugin.py
+++ b/src/PIL/FliImagePlugin.py
@@ -32,6 +32,7 @@ def _accept(prefix: bytes) -> bool:
     return (
         len(prefix) >= 6
         and i16(prefix, 4) in [0xAF11, 0xAF12]
+        and i16(prefix, 12) == 8  # 8-bit colour
         and i16(prefix, 14) in [0, 3]  # flags
     )