diff --git a/src/V3Param.cpp b/src/V3Param.cpp
index 5b8f0ee2b..9ecfb4782 100644
--- a/src/V3Param.cpp
+++ b/src/V3Param.cpp
@@ -958,6 +958,9 @@ class ParamProcessor final {
         m_paramIndex.clear();
         for (AstNode* stmtp = classp->stmtsp(); stmtp; stmtp = stmtp->nextp()) {
             if (AstParamTypeDType* paramTypep = VN_CAST(stmtp, ParamTypeDType)) {
+                // Only consider formal class type parameters (generic parameters),
+                // not localparam type declarations inside the class body.
+                if (!paramTypep->isGParam()) continue;
                 m_paramIndex.emplace(paramTypep, m_classParams.size());
                 m_classParams.emplace_back(paramTypep, -1);
             }
@@ -1194,6 +1197,24 @@ public:
     VL_UNCOPYABLE(ParamProcessor);
 };
 
+//######################################################################
+// This visitor records classes that are referenced with parameter pins
+class ClassPinsMarkVisitor final : public VNVisitorConst {
+
+public:
+    explicit ClassPinsMarkVisitor(AstNetlist* netlistp) { iterateConst(netlistp); }
+
+    void visit(AstClassOrPackageRef* nodep) override {
+        if (nodep->paramsp()) {
+            if (AstClass* const classp = VN_CAST(nodep->classOrPackageSkipp(), Class)) {
+                classp->user3p(classp);
+            }
+        }
+    }
+    void visit(AstClass* nodep) override {}  // don't iterate inside classes
+    void visit(AstNode* nodep) override { iterateChildrenConst(nodep); }
+};
+
 //######################################################################
 // Process parameter visitor
 
@@ -1661,6 +1682,9 @@ public:
         // Relies on modules already being in top-down-order
         iterate(netlistp);
 
+        // Mark classes which cannot be removed because they are still referenced
+        ClassPinsMarkVisitor markVisitor{netlistp};
+
         relinkDots();
 
         // Re-sort module list to be in topological order and fix-up incorrect levels. We need to
diff --git a/test_regress/t/t_bug6418.py b/test_regress/t/t_bug6418.py
new file mode 100755
index 000000000..319c0ff4a
--- /dev/null
+++ b/test_regress/t/t_bug6418.py
@@ -0,0 +1,16 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2025 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('vlt')
+
+test.compile()
+
+test.passes()
diff --git a/test_regress/t/t_bug6418.v b/test_regress/t/t_bug6418.v
new file mode 100644
index 000000000..70ed0e502
--- /dev/null
+++ b/test_regress/t/t_bug6418.v
@@ -0,0 +1,48 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2025 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+package pk1;
+  typedef struct packed {
+    int AddrBits;
+    int DataBits;
+  } cfg_t;
+endpackage
+
+virtual class a_class_t #(
+    parameter pk1::cfg_t CFG = 0
+);
+  // verilator lint_off ASCRANGE
+  localparam type addr_t = logic [CFG.AddrBits-1:0];
+  localparam type data_t = logic [CFG.DataBits-1:0];
+  // verilator lint_on ASCRANGE
+
+  typedef struct packed {
+    addr_t addr;
+    data_t data;
+  } pkt_t;
+endclass
+
+interface ifc #(
+    parameter pk1::cfg_t CFG = 0
+);
+  a_class_t #(CFG)::pkt_t p;
+endinterface
+
+module a_to_b #(
+    parameter pk1::cfg_t ACFG = 0
+) (
+    ifc bus
+);
+  // sturf
+endmodule
+
+module t;
+  localparam pk1::cfg_t ACFG = '{AddrBits : 64, DataBits : 64};
+
+  ifc #(.CFG(ACFG)) the_bus ();
+
+  a_to_b #(ACFG) a_to_b (.bus(the_bus));
+endmodule