diff --git a/pkgs/additional/koreader-from-src/sources.nix b/pkgs/additional/koreader-from-src/sources.nix
index 710fa8d2..b4741225 100644
--- a/pkgs/additional/koreader-from-src/sources.nix
+++ b/pkgs/additional/koreader-from-src/sources.nix
@@ -129,7 +129,14 @@ in
       source.url = "https://github.com/DanBloomberg/leptonica.git";
       source.rev = "1.74.1";
       source.hash = "sha256-SDXKam768xvZZvTbXe3sssvZyeLEEiY97Vrzx8hoc6g=";
-      # package = leptonica;  # k2pdf needs leptonica src.  # cp -f /build/koreader/base/thirdparty/libk2pdfopt/build/aarch64-unknown-linux-gnu/libk2pdfopt-prefix/src/libk2pdfopt/leptonica_mod/dewarp2.c
+      # k2pdf needs leptonica src, because it actually patches it and builds it itself
+      # `cp -f $(LEPTONICA_MOD)/dewarp2.c $(LEPTONICA_DIR)/src/dewarp2.c`
+      #  i.e. cp -f /build/koreader/base/thirdparty/libk2pdfopt/build/aarch64-unknown-linux-gnu/libk2pdfopt-prefix/src/libk2pdfopt/leptonica_mod/dewarp2.c ...
+      # k2pdf uses an old leptonica -- like 2015-2017-ish.
+      # seems it can be at least partially updated, by replacing `numaGetMedianVariation` with `numaGetMedianDevFromMedian` (drop-in replacement)
+      # and replacing references to `liblept.so` with `libleptonica.so`,
+      # but eventually this requires patching the tesseract Makefiles. could get intense, idk.
+      # package = leptonica;
     };
     # libjpeg-turbo = {
     #   source.url = "https://github.com/libjpeg-turbo/libjpeg-turbo.git";