diff --git a/crates/fayalite/src/sim/compiler.rs b/crates/fayalite/src/sim/compiler.rs
index 282507f..a098151 100644
--- a/crates/fayalite/src/sim/compiler.rs
+++ b/crates/fayalite/src/sim/compiler.rs
@@ -3974,10 +3974,13 @@ impl Compiler {
                 .compile_expr(instantiated_module_or_global, Expr::canonical(expr.arg()))
                 .map_ty(TraceAsString::from_canonical)
                 .inner(),
-            ExprEnum::StructuralEq(expr) => self.compile_expr(
-                instantiated_module_or_global,
-                Expr::canonical(expr.lhs().cast_to_bits().cmp_eq(expr.rhs().cast_to_bits())),
-            ),
+            ExprEnum::StructuralEq(expr) => {
+                // FIXME: actually ignore enum padding
+                self.compile_expr(
+                    instantiated_module_or_global,
+                    Expr::canonical(expr.lhs().cast_to_bits().cmp_eq(expr.rhs().cast_to_bits())),
+                )
+            }
             ExprEnum::ModuleIO(expr) => self
                 .compile_value(TargetInInstantiatedModuleOrGlobal::from_target(
                     instantiated_module_or_global,
diff --git a/crates/fayalite/tests/sim.rs b/crates/fayalite/tests/sim.rs
index 223c4bc..343b87b 100644
--- a/crates/fayalite/tests/sim.rs
+++ b/crates/fayalite/tests/sim.rs
@@ -3749,3 +3749,67 @@ at module-XXXXXXXXXX.rs:12:1: in InstantiatedModule(formal_counter: formal_count
         }
     }
 }
+
+#[hdl_module(outline_generated)]
+pub fn enum_structural_eq() {
+    #[hdl]
+    let a: HdlOption<UInt<2>> = m.input();
+    #[hdl]
+    let b: HdlOption<UInt<2>> = m.input();
+    #[hdl]
+    let eq: Bool = m.output();
+    #[hdl]
+    let structural_eq: Bool = m.output();
+    #[hdl]
+    let bit_eq: Bool = m.output();
+
+    connect(eq, a.cmp_eq(b));
+    // explicitly use StructuralEq (though cmp_eq also uses it above)
+    connect(
+        structural_eq,
+        fayalite::expr::ops::StructuralEq::new(Expr::canonical(a), Expr::canonical(b)),
+    );
+    connect(bit_eq, a.cast_to_bits().cmp_eq(b.cast_to_bits()));
+}
+
+#[test]
+fn test_enum_structural_eq() {
+    let _n = SourceLocation::normalize_files_for_tests();
+    let mut sim = Simulation::new(enum_structural_eq());
+    let _checked_vcd_output =
+        checked_vcd_output!(&mut sim, "tests/sim/expected/test_enum_structural_eq.vcd");
+    for a in 0..8u8 {
+        for b in 0..8u8 {
+            dbg!(a);
+            dbg!(b);
+            let a_sim_value = a.cast_to(UInt[3]).cast_bits_to(sim.io().a.ty());
+            let b_sim_value = b.cast_to(UInt[3]).cast_bits_to(sim.io().b.ty());
+            dbg!(&a_sim_value);
+            dbg!(&b_sim_value);
+            sim.write(sim.io().a, a_sim_value);
+            sim.write(sim.io().b, b_sim_value);
+            let a_with_zeroed_padding = if (a & 1) != 0 { a } else { 0 };
+            let b_with_zeroed_padding = if (b & 1) != 0 { b } else { 0 };
+            dbg!(a_with_zeroed_padding);
+            dbg!(b_with_zeroed_padding);
+            let expected_eq = a_with_zeroed_padding == b_with_zeroed_padding;
+            let expected_structural_eq = a_with_zeroed_padding == b_with_zeroed_padding;
+            let expected_bit_eq = a == b;
+            dbg!(expected_eq);
+            dbg!(expected_structural_eq);
+            dbg!(expected_bit_eq);
+            sim.advance_time(SimDuration::from_micros(1));
+            assert_eq!(sim.read_bool(sim.io().eq), expected_eq);
+            assert_eq!(
+                sim.read_bool(sim.io().structural_eq),
+                expected_structural_eq
+            );
+            assert_eq!(sim.read_bool(sim.io().bit_eq), expected_bit_eq);
+        }
+    }
+    let sim_debug = format!("{sim:#?}");
+    println!("#######\n{sim_debug}\n#######");
+    if sim_debug != include_str!("sim/expected/test_enum_structural_eq.txt") {
+        panic!();
+    }
+}
diff --git a/crates/fayalite/tests/sim/expected/test_enum_structural_eq.txt b/crates/fayalite/tests/sim/expected/test_enum_structural_eq.txt
new file mode 100644
index 0000000..e69de29
diff --git a/crates/fayalite/tests/sim/expected/test_enum_structural_eq.vcd b/crates/fayalite/tests/sim/expected/test_enum_structural_eq.vcd
new file mode 100644
index 0000000..ddb10e7
--- /dev/null
+++ b/crates/fayalite/tests/sim/expected/test_enum_structural_eq.vcd
@@ -0,0 +1,33 @@
+$timescale 1 ps $end
+$scope module enum_structural_eq $end
+$scope struct a $end
+$var string 1 +LxwI \$tag $end
+$var wire 2 {bf!u HdlSome $end
+$upscope $end
+$scope struct b $end
+$var string 1 O%@#" \$tag $end
+$var wire 2 ]xpB, HdlSome $end
+$upscope $end
+$var wire 1 Yp4xI eq $end
+$var wire 1 >R/<6 structural_eq $end
+$var wire 1 ,}=e] bit_eq $end
+$upscope $end
+$enddefinitions $end
+$dumpvars
+sHdlNone\x20(0) +LxwI
+b0 {bf!u
+sHdlNone\x20(0) O%@#"
+b0 ]xpB,
+1Yp4xI
+1>R/<6
+1,}=e]
+$end
+#1000000
+sHdlSome\x20(1) O%@#"
+0Yp4xI
+0>R/<6
+0,}=e]
+#2000000
+sHdlNone\x20(0) O%@#"
+b1 ]xpB,
+#3000000