diff --git a/pkgs/build-support/writers/default.nix b/pkgs/build-support/writers/default.nix
index 47919c251af1..5a70bcbe3cf6 100644
--- a/pkgs/build-support/writers/default.nix
+++ b/pkgs/build-support/writers/default.nix
@@ -15,12 +15,12 @@ rec {
       name = last (builtins.split "/" nameOrPath);
     in
 
-    pkgs.runCommandLocal name (if (types.str.check content) then {
-      inherit content interpreter;
-      passAsFile = [ "content" ];
-    } else {
+    pkgs.runCommandLocal name (if types.path.check content then {
       inherit interpreter;
       contentPath = content;
+    } else {
+      inherit content interpreter;
+      passAsFile = [ "content" ];
     }) ''
       # On darwin a script cannot be used as an interpreter in a shebang but
       # there doesn't seem to be a limit to the size of shebang and multiple