diff --git a/pkgs/build-support/src-only/default.nix b/pkgs/build-support/src-only/default.nix
index f8c3068d6c73..b732c6156041 100644
--- a/pkgs/build-support/src-only/default.nix
+++ b/pkgs/build-support/src-only/default.nix
@@ -69,12 +69,15 @@ if lib.isDerivation attrs && attrs ? overrideAttrs then
   attrs.overrideAttrs (_finalAttrs: prevAttrs: argsToOverride prevAttrs)
 else
   let
-    # TODO(@sternenseemann): remove drvAttrs special casing
     # If we don't have overrideAttrs, it is extremely unlikely that we are seeing
     # a derivation constructed by stdenv.mkDerivation. Since srcOnly assumes
     # that we are using stdenv's setup.sh, it therefore doesn't make sense to
     # have derivation specific logic in this branch.
-    args = attrs.drvAttrs or attrs;
+    # TODO(@sternenseemann): remove drvAttrs special casing in NixOS 26.05
+    args =
+      lib.warnIf (lib.isDerivation attrs)
+        "srcOnly: derivations not created by a variant of stdenv.mkDerivation are not supported. Code relying on behaviour of srcOnly with non-stdenv derivations may break in the future."
+        attrs.drvAttrs or attrs;
     stdenv = args.stdenv or (lib.warn "srcOnly: stdenv not provided, using stdenvNoCC" stdenvNoCC);
     drv = stdenv.mkDerivation (args // argsToOverride args);
   in