diff --git a/pkgs/stdenv/generic/check-meta.nix b/pkgs/stdenv/generic/check-meta.nix
index 8544d932f81..be98b1fce32 100644
--- a/pkgs/stdenv/generic/check-meta.nix
+++ b/pkgs/stdenv/generic/check-meta.nix
@@ -162,7 +162,7 @@ let
 
   checkMetaAttr = k: v:
     if metaTypes?${k} then
-      if metaTypes.${k}.check v then null else "key '${k}' has a value ${v} of an invalid type ${builtins.typeOf v}; expected ${metaTypes.${k}.description}"
+      if metaTypes.${k}.check v then null else "key '${k}' has a value ${toString v} of an invalid type ${builtins.typeOf v}; expected ${metaTypes.${k}.description}"
     else "key '${k}' is unrecognized; expected one of: \n\t      [${lib.concatMapStringsSep ", " (x: "'${x}'") (lib.attrNames metaTypes)}]";
   checkMeta = meta: if shouldCheckMeta then lib.remove null (lib.mapAttrsToList checkMetaAttr meta) else [];