diff --git a/pkgs/build-support/docker/default.nix b/pkgs/build-support/docker/default.nix
index 5bbf1b63f2b0..89510cd6330c 100644
--- a/pkgs/build-support/docker/default.nix
+++ b/pkgs/build-support/docker/default.nix
@@ -536,7 +536,7 @@ rec {
         passthru.layer = layer;
         passthru.imageTag =
           if tag != null
-            then lib.toLower tag
+            then tag
             else
               lib.head (lib.strings.splitString "-" (baseNameOf result.outPath));
         # Docker can't be made to run darwin binaries