diff --git a/pngtrans.c b/pngtrans.c
index a6cab0cdf0..d8ab362d66 100644
--- a/pngtrans.c
+++ b/pngtrans.c
@@ -848,6 +848,16 @@ png_set_user_transform_info(png_struct *png_ptr, void *user_transform_ptr,
    }
 #endif
 
+   if (user_transform_depth != 0 &&
+       user_transform_depth != 1 && user_transform_depth != 2 &&
+       user_transform_depth != 4 && user_transform_depth != 8 &&
+       user_transform_depth != 16)
+   {
+      png_app_error(png_ptr,
+          "png_set_user_transform_info: invalid user_transform_depth");
+      return;
+   }
+
    png_ptr->user_transform_ptr = user_transform_ptr;
    png_ptr->user_transform_depth = (png_byte)user_transform_depth;
    png_ptr->user_transform_channels = (png_byte)user_transform_channels;