diff --git a/pkgs/build-support/fetchgit/default.nix b/pkgs/build-support/fetchgit/default.nix
index 14636e43ade89e..f2b4726fef09da 100644
--- a/pkgs/build-support/fetchgit/default.nix
+++ b/pkgs/build-support/fetchgit/default.nix
@@ -65,7 +65,7 @@ assert nonConeMode -> (sparseCheckout != []);
 let
   revWithTag =
     let
-      warningMsg = "fetchgit requires either `rev` xor `tag`.";
+      warningMsg = "fetchgit requires one of either `rev` or `tag` to be provided (not both).";
       otherIsNull = other: lib.assertMsg (other == null) warningMsg;
     in
     if tag != null then
diff --git a/pkgs/build-support/fetchgithub/default.nix b/pkgs/build-support/fetchgithub/default.nix
index 03c39a1fba9398..f80e0129553367 100644
--- a/pkgs/build-support/fetchgithub/default.nix
+++ b/pkgs/build-support/fetchgithub/default.nix
@@ -14,7 +14,7 @@ lib.makeOverridable (
 , ... # For hash agility
 }@args:
 
-assert (lib.assertMsg (lib.xor (tag == null) (rev == null)) "fetchFromGitHub requires either `rev` xor `tag`.");
+assert (lib.assertMsg (lib.xor (tag == null) (rev == null)) "fetchFromGitHub requires one of either `rev` or `tag` to be provided (not both).");
 
 let