diff --git a/src/V3Const.cpp b/src/V3Const.cpp
index f43f31afe..b76c8244b 100644
--- a/src/V3Const.cpp
+++ b/src/V3Const.cpp
@@ -2053,7 +2053,7 @@ private:
                 VL_DO_DANGLING(nodep->unlinkFrBack()->deleteTree(), nodep);
                 return true;
             }
-        } else if (m_doV && VN_IS(nodep->lhsp(), Concat)) {
+        } else if (m_doV && VN_IS(nodep->lhsp(), Concat) && nodep->isTreePureRecurse()) {
             bool need_temp = false;
             if (m_warn && !VN_IS(nodep, AssignDly)) {  // Is same var on LHS and RHS?
                 // Note only do this (need user4) when m_warn, which is
diff --git a/src/V3Subst.cpp b/src/V3Subst.cpp
index eecb39579..38ebafb6a 100644
--- a/src/V3Subst.cpp
+++ b/src/V3Subst.cpp
@@ -198,7 +198,10 @@ private:
         }
     }
     void visit(AstConst*) override {}  // Accelerate
-    void visit(AstNode* nodep) override { iterateChildren(nodep); }
+    void visit(AstNode* nodep) override {
+        if (!nodep->isPure()) m_ok = false;
+        iterateChildren(nodep);
+    }
 
 public:
     // CONSTRUCTORS