diff --git a/package.nix b/package.nix
index dd37809d0..727f5e646 100644
--- a/package.nix
+++ b/package.nix
@@ -167,6 +167,10 @@ in {
           ./doc/manual
         ] ++ lib.optionals enableInternalAPIDocs [
           ./doc/internal-api
+          # Source might not be compiled, but still must be available
+          # for Doxygen to gather comments.
+          ./src
+          ./tests/unit
         ] ++ lib.optionals buildUnitTests [
           ./tests/unit
         ] ++ lib.optionals doInstallCheck [