diff --git a/pkgs/development/compilers/opensmalltalk-vm/default.nix b/pkgs/development/compilers/opensmalltalk-vm/default.nix
index 1f392075b94a..82481a8e17eb 100644
--- a/pkgs/development/compilers/opensmalltalk-vm/default.nix
+++ b/pkgs/development/compilers/opensmalltalk-vm/default.nix
@@ -180,5 +180,7 @@ let
 
   platform = stdenv.targetPlatform.system;
 in
-  vmsByPlatform.${platform} or
-    (throw "Unsupported platform ${platform}: only the following platforms are supported: ${builtins.attrNames vmsByPlatform}")
+  vmsByPlatform.${platform} or throw (
+    "Unsupported platform ${platform}: only the following platforms are supported: " +
+    builtins.toString (builtins.attrNames vmsByPlatform)
+  )