diff --git a/pkgs/build-support/docker/default.nix b/pkgs/build-support/docker/default.nix
index 6b8a03932f5b..86bd7e312cbd 100644
--- a/pkgs/build-support/docker/default.nix
+++ b/pkgs/build-support/docker/default.nix
@@ -637,7 +637,7 @@ rec {
             if tag != null
             then tag
             else
-              lib.head (lib.strings.splitString "-" (baseNameOf result.outPath));
+              lib.head (lib.strings.splitString "-" (baseNameOf (builtins.unsafeDiscardStringContext result.outPath)));
         } ''
         ${lib.optionalString (tag == null) ''
           outName="$(basename "$out")"
@@ -1001,7 +1001,7 @@ rec {
               if tag != null
               then tag
               else
-                lib.head (lib.strings.splitString "-" (baseNameOf conf.outPath));
+                lib.head (lib.strings.splitString "-" (baseNameOf (builtins.unsafeDiscardStringContext conf.outPath)));
             paths = buildPackages.referencesByPopularity overallClosure;
             nativeBuildInputs = [ jq ];
           } ''