diff --git a/pkgs/build-support/fetchgit/default.nix b/pkgs/build-support/fetchgit/default.nix
index abd9fb23e052..3d73eae9821e 100644
--- a/pkgs/build-support/fetchgit/default.nix
+++ b/pkgs/build-support/fetchgit/default.nix
@@ -54,16 +54,16 @@ lib.makeOverridable (
 */
 
 assert deepClone -> leaveDotGit;
-assert nonConeMode -> !(sparseCheckout == "" || sparseCheckout == []);
+assert nonConeMode -> (sparseCheckout != []);
 
 if md5 != "" then
   throw "fetchgit does not support md5 anymore, please use sha256"
 else if hash != "" && sha256 != "" then
   throw "Only one of sha256 or hash can be set"
+else if builtins.isString sparseCheckout then
+  # Changed to throw on 2023-06-04
+  throw "Please provide directories/patterns for sparse checkout as a list of strings. Passing a (multi-line) string is not supported any more."
 else
-# Added 2022-11-12
-lib.warnIf (builtins.isString sparseCheckout)
-  "Please provide directories/patterns for sparse checkout as a list of strings. Support for passing a (multi-line) string is deprecated and will be removed in the next release."
 stdenvNoCC.mkDerivation {
   inherit name;
   builder = ./builder.sh;
@@ -84,7 +84,7 @@ stdenvNoCC.mkDerivation {
   # git-sparse-checkout(1) says:
   # > When the --stdin option is provided, the directories or patterns are read
   # > from standard in as a newline-delimited list instead of from the arguments.
-  sparseCheckout = if builtins.isString sparseCheckout then sparseCheckout else builtins.concatStringsSep "\n" sparseCheckout;
+  sparseCheckout = builtins.concatStringsSep "\n" sparseCheckout;
 
   inherit url rev leaveDotGit fetchLFS fetchSubmodules deepClone branchName nonConeMode postFetch;
 
diff --git a/pkgs/build-support/fetchgithub/default.nix b/pkgs/build-support/fetchgithub/default.nix
index fc09c211b426..faa338b672f0 100644
--- a/pkgs/build-support/fetchgithub/default.nix
+++ b/pkgs/build-support/fetchgithub/default.nix
@@ -25,7 +25,7 @@ let
   };
   passthruAttrs = removeAttrs args [ "owner" "repo" "rev" "fetchSubmodules" "forceFetchGit" "private" "githubBase" "varPrefix" ];
   varBase = "NIX${if varPrefix == null then "" else "_${varPrefix}"}_GITHUB_PRIVATE_";
-  useFetchGit = fetchSubmodules || (leaveDotGit == true) || deepClone || forceFetchGit || !(sparseCheckout == "" || sparseCheckout == []);
+  useFetchGit = fetchSubmodules || (leaveDotGit == true) || deepClone || forceFetchGit || (sparseCheckout != []);
   # We prefer fetchzip in cases we don't need submodules as the hash
   # is more stable in that case.
   fetcher = if useFetchGit then fetchgit else fetchzip;