diff --git a/modules/conop/src/conop.cc b/modules/conop/src/conop.cc
index e2fc45e2e227f32d4d14b75181170ab4604e68c4..76273ce5f6612956bc5fd858a2634a306441161d 100644
--- a/modules/conop/src/conop.cc
+++ b/modules/conop/src/conop.cc
@@ -181,7 +181,7 @@ public:
   virtual bool VisitResidue(const mol::ResidueHandle& res)
   {
     String key=builder_->IdentifyResidue(res);
-    if (key=="UNK") {
+    if (key=="UNK" && res.GetKey()!="UNK") {
       unk_res_[res.GetKey()]+=1;
     }
     builder_->FillResidueProps(res);