diff --git a/Changes b/Changes
index 74f94da5c..0cc7392f2 100644
--- a/Changes
+++ b/Changes
@@ -102,6 +102,7 @@ Verilator 5.029 devel
 * Fix struct literal on pattern assignment (#5552) (#5559). [Todd Strader]
 * Fix build on gcc when using the Spack wrapper (#5555). [Eric Müller]
 * Fix enum name method (#5563). [Todd Strader]
+* Fix `$countbits` in assert with non-tristates (#5566). [Shou-Li Hsu]
 
 
 Verilator 5.028 2024-08-21
diff --git a/src/V3Tristate.cpp b/src/V3Tristate.cpp
index b30be761d..6663c879e 100644
--- a/src/V3Tristate.cpp
+++ b/src/V3Tristate.cpp
@@ -1433,7 +1433,6 @@ class TristateVisitor final : public TristateBaseVisitor {
         dropop[1] = VN_IS(nodep->thsp(), Const) && VN_AS(nodep->thsp(), Const)->num().isAnyZ();
         dropop[2] = VN_IS(nodep->fhsp(), Const) && VN_AS(nodep->fhsp(), Const)->num().isAnyZ();
         UINFO(4, " COUNTBITS(" << dropop[0] << dropop[1] << dropop[2] << " " << nodep << endl);
-        const AstVarRef* const varrefp = VN_AS(nodep->lhsp(), VarRef);  // Input variable
         if (m_graphing) {
             iterateAndNextNull(nodep->lhsp());
             if (!dropop[0]) iterateAndNextNull(nodep->rhsp());
@@ -1454,7 +1453,8 @@ class TristateVisitor final : public TristateBaseVisitor {
                 // do so at present, we only compare if there is a z in the equation. Otherwise
                 // we'd need to attach an enable to every signal, then optimize them away later
                 // when we determine the signal has no tristate
-                if (!VN_IS(nodep->lhsp(), VarRef)) {
+                const AstVarRef* const varrefp = VN_CAST(nodep->lhsp(), VarRef);  // Input variable
+                if (!varrefp) {
                     nodep->v3warn(E_UNSUPPORTED, "Unsupported LHS tristate construct: "
                                                      << nodep->prettyTypeName());
                     return;
diff --git a/test_regress/t/t_math_countbits_tri.py b/test_regress/t/t_math_countbits_tri.py
new file mode 100755
index 000000000..2c4ffdce2
--- /dev/null
+++ b/test_regress/t/t_math_countbits_tri.py
@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2024 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('simulator')
+
+test.compile(verilator_flags2=['--assert'])
+
+test.execute()
+
+test.passes()
diff --git a/test_regress/t/t_math_countbits_tri.v b/test_regress/t/t_math_countbits_tri.v
new file mode 100644
index 000000000..421ce6e5d
--- /dev/null
+++ b/test_regress/t/t_math_countbits_tri.v
@@ -0,0 +1,38 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2024 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+module t(/*AUTOARG*/
+   // Outputs
+   num_zeros, num_ones,
+   // Inputs
+   clk, reset_l, vec
+   );
+
+   input logic clk;
+   input logic reset_l;
+   input logic [7:0] vec;
+   output logic [7:0] num_zeros;
+   output logic [7:0] num_ones;
+
+   always_comb begin
+      num_zeros = '0;
+      num_ones = '0;
+      for (int i = 0; i < 8; i++) begin
+         if (vec[i] == 0) begin
+            num_zeros++;
+         end else begin
+            num_ones++;
+         end
+      end
+   end
+   assert property (@(negedge clk) disable iff (~reset_l) (num_ones == $countones(vec)));
+   assert property (@(negedge clk) disable iff (~reset_l) (num_zeros == $countbits(vec, '0)));
+   initial begin
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+
+endmodule