diff --git a/src/V3DfgAstToDfg.cpp b/src/V3DfgAstToDfg.cpp
index 57e310df7..18df9a1b0 100644
--- a/src/V3DfgAstToDfg.cpp
+++ b/src/V3DfgAstToDfg.cpp
@@ -233,6 +233,13 @@ class AstToDfgVisitor final : public VNVisitor {
     // Containers to descend through to find logic constructs
     void visit(AstNetlist* nodep) override { iterateAndNextNull(nodep->modulesp()); }
     void visit(AstModule* nodep) override { iterateAndNextNull(nodep->stmtsp()); }
+    void visit(AstIface* nodep) override {
+        if (!nodep->hasVirtualRef()) {
+            iterateAndNextNull(nodep->stmtsp());
+        } else {
+            markReferenced(nodep);
+        }
+    }
     void visit(AstTopScope* nodep) override { iterate(nodep->scopep()); }
     void visit(AstScope* nodep) override { iterateChildren(nodep); }
     void visit(AstActive* nodep) override {