gistfile1.txt

diff --git a/src/6model/reprs/P6opaque.c b/src/6model/reprs/P6opaque.c
index acbfa96..db21971 100644
--- a/src/6model/reprs/P6opaque.c
+++ b/src/6model/reprs/P6opaque.c
@@ -383,6 +383,8 @@ static void bind_attribute(MVMThreadContext *tc, MVMSTable *st, MVMObject *root,
             break;
         }
         case MVM_reg_str: {
+            if (value_reg.s && ((MVMObject *)value_reg.s)->st->REPR->ID != MVM_REPR_ID_MVMString)
+                MVM_exception_throw_adhoc(tc, "P6opaque: string is not a string");
             if (attr_st)
                 attr_st->REPR->box_funcs.set_str(tc, attr_st, root,
                     (char *)data + repr_data->attribute_offsets[slot],