Index: generic/predefined.xotcl
===================================================================
diff -u -ra38906707b8e508b97f01c9b68071c927c2a5d0f -rc942f4e117d2aa3c8594702e0476a3f73a4147df
--- generic/predefined.xotcl	(.../predefined.xotcl)	(revision a38906707b8e508b97f01c9b68071c927c2a5d0f)
+++ generic/predefined.xotcl	(.../predefined.xotcl)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
@@ -850,18 +850,19 @@
   ::xotcl::Slot method type=hasmixin {name value arg} {
     if {![::xotcl::is $value hasmixin $arg]} {
       error "Value '$value' of $name has not mixin $arg"
+      error "expected object with mixin $arg but got \"$value\" for parameter $name"
     }
     return $value
   }
   ::xotcl::Slot method type=baseclass {name value} {
     if {![::xotcl::is $value baseclass]} {
-      error "Value '$value' of $name is not a baseclass"
+      error "expected baseclass but got \"$value\" for parameter $name"
     }
     return $value
   }
   ::xotcl::Slot method type=metaclass {name value} {
     if {![::xotcl::is $value metaclass]} {
-      error "Value '$value' of $name is not a metaclass"
+      error "expected metaclass but got \"$value\" for parameter $name"
     }
     return $value
   }