diff --git a/crates/fayalite/src/firrtl.rs b/crates/fayalite/src/firrtl.rs
index 4a1547d..79db858 100644
--- a/crates/fayalite/src/firrtl.rs
+++ b/crates/fayalite/src/firrtl.rs
@@ -1956,6 +1956,15 @@ impl<'a> Exporter<'a> {
                     rhs,
                     source_location,
                 }) => {
+                    if Expr::ty(lhs) != Expr::ty(rhs) {
+                        writeln!(
+                            body,
+                            "{indent}; connect different types:\n{indent}; lhs: {:?}\n{indent}; rhs: {:?}",
+                            Expr::ty(lhs),
+                            Expr::ty(rhs),
+                        )
+                        .unwrap();
+                    }
                     let lhs = self.expr(lhs, &definitions, false);
                     let rhs = self.expr(rhs, &definitions, false);
                     writeln!(
diff --git a/crates/fayalite/tests/module.rs b/crates/fayalite/tests/module.rs
index 9d5a898..4dfeca5 100644
--- a/crates/fayalite/tests/module.rs
+++ b/crates/fayalite/tests/module.rs
@@ -722,6 +722,9 @@ circuit check_struct_enum_match:
                     A:
                         connect o[0], UInt<8>(0h17) @[module-XXXXXXXXXX.rs 7:1]
                     B(_match_arm_value):
+                        ; connect different types:
+                        ; lhs: UInt<8>
+                        ; rhs: UInt<9>
                         connect o[0], add(_match_arm_value, UInt<8>(0h2)) @[module-XXXXXXXXXX.rs 8:1]
                     C(_match_arm_value_1):
                         connect o[0], UInt<8>(0h17) @[module-XXXXXXXXXX.rs 7:1]
@@ -738,6 +741,9 @@ circuit check_struct_enum_match:
             B(_match_arm_value_4):
                 connect o[2], _match_arm_value_4 @[module-XXXXXXXXXX.rs 15:1]
             C(_match_arm_value_5):
+                ; connect different types:
+                ; lhs: UInt<8>
+                ; rhs: UInt<1>
                 connect o[2], _match_arm_value_5[1] @[module-XXXXXXXXXX.rs 16:1]
         match i2: @[module-XXXXXXXXXX.rs 17:1]
             A:
@@ -752,6 +758,9 @@ circuit check_struct_enum_match:
             B(_match_arm_value_8):
                 connect o[4], UInt<8>(0h1) @[module-XXXXXXXXXX.rs 23:1]
             C(_match_arm_value_9):
+                ; connect different types:
+                ; lhs: UInt<8>
+                ; rhs: UInt<1>
                 connect o[4], _match_arm_value_9[2] @[module-XXXXXXXXXX.rs 24:1]
 ",
     };
@@ -777,6 +786,9 @@ circuit check_struct_enum_match:
                     A:
                         connect o[0], UInt<8>(0h17) @[module-XXXXXXXXXX.rs 7:1]
                     B:
+                        ; connect different types:
+                        ; lhs: UInt<8>
+                        ; rhs: UInt<9>
                         connect o[0], add(bits(i2.body, 7, 0), UInt<8>(0h2)) @[module-XXXXXXXXXX.rs 8:1]
                     C:
                         connect o[0], UInt<8>(0h17) @[module-XXXXXXXXXX.rs 7:1]
@@ -801,6 +813,9 @@ circuit check_struct_enum_match:
                 connect _cast_bits_to_array_expr[1], _cast_bits_to_array_expr_flattened[1]
                 connect _cast_bits_to_array_expr_flattened[2], bits(bits(i2.body, 2, 0), 2, 2)
                 connect _cast_bits_to_array_expr[2], _cast_bits_to_array_expr_flattened[2]
+                ; connect different types:
+                ; lhs: UInt<8>
+                ; rhs: UInt<1>
                 connect o[2], _cast_bits_to_array_expr[1] @[module-XXXXXXXXXX.rs 16:1]
         match i2.tag: @[module-XXXXXXXXXX.rs 17:1]
             A:
@@ -823,6 +838,9 @@ circuit check_struct_enum_match:
                 connect _cast_bits_to_array_expr_1[1], _cast_bits_to_array_expr_flattened_1[1]
                 connect _cast_bits_to_array_expr_flattened_1[2], bits(bits(i2.body, 2, 0), 2, 2)
                 connect _cast_bits_to_array_expr_1[2], _cast_bits_to_array_expr_flattened_1[2]
+                ; connect different types:
+                ; lhs: UInt<8>
+                ; rhs: UInt<1>
                 connect o[4], _cast_bits_to_array_expr_1[2] @[module-XXXXXXXXXX.rs 24:1]
 ",
     };
@@ -843,6 +861,9 @@ circuit check_struct_enum_match:
             when eq(i2.tag, UInt<2>(0h0)): @[module-XXXXXXXXXX.rs 6:1]
                 connect o[0], UInt<8>(0h17) @[module-XXXXXXXXXX.rs 7:1]
             else when eq(i2.tag, UInt<2>(0h1)): @[module-XXXXXXXXXX.rs 6:1]
+                ; connect different types:
+                ; lhs: UInt<8>
+                ; rhs: UInt<9>
                 connect o[0], add(bits(i2.body, 7, 0), UInt<8>(0h2)) @[module-XXXXXXXXXX.rs 8:1]
             else:
                 connect o[0], UInt<8>(0h17) @[module-XXXXXXXXXX.rs 7:1]
@@ -865,6 +886,9 @@ circuit check_struct_enum_match:
             connect _cast_bits_to_array_expr[1], _cast_bits_to_array_expr_flattened[1]
             connect _cast_bits_to_array_expr_flattened[2], bits(bits(i2.body, 2, 0), 2, 2)
             connect _cast_bits_to_array_expr[2], _cast_bits_to_array_expr_flattened[2]
+            ; connect different types:
+            ; lhs: UInt<8>
+            ; rhs: UInt<1>
             connect o[2], _cast_bits_to_array_expr[1] @[module-XXXXXXXXXX.rs 16:1]
         when eq(i2.tag, UInt<2>(0h0)): @[module-XXXXXXXXXX.rs 17:1]
             connect o[3], UInt<8>(0h0) @[module-XXXXXXXXXX.rs 18:1]
@@ -885,6 +909,9 @@ circuit check_struct_enum_match:
             connect _cast_bits_to_array_expr_1[1], _cast_bits_to_array_expr_flattened_1[1]
             connect _cast_bits_to_array_expr_flattened_1[2], bits(bits(i2.body, 2, 0), 2, 2)
             connect _cast_bits_to_array_expr_1[2], _cast_bits_to_array_expr_flattened_1[2]
+            ; connect different types:
+            ; lhs: UInt<8>
+            ; rhs: UInt<1>
             connect o[4], _cast_bits_to_array_expr_1[2] @[module-XXXXXXXXXX.rs 24:1]
 ",
     };
@@ -903,6 +930,9 @@ circuit check_struct_enum_match:
             when eq(bits(i2, 1, 0), UInt<2>(0h0)): @[module-XXXXXXXXXX.rs 6:1]
                 connect o[0], UInt<8>(0h17) @[module-XXXXXXXXXX.rs 7:1]
             else when eq(bits(i2, 1, 0), UInt<2>(0h1)): @[module-XXXXXXXXXX.rs 6:1]
+                ; connect different types:
+                ; lhs: UInt<8>
+                ; rhs: UInt<9>
                 connect o[0], add(bits(bits(i2, 9, 2), 7, 0), UInt<8>(0h2)) @[module-XXXXXXXXXX.rs 8:1]
             else:
                 connect o[0], UInt<8>(0h17) @[module-XXXXXXXXXX.rs 7:1]
@@ -925,6 +955,9 @@ circuit check_struct_enum_match:
             connect _cast_bits_to_array_expr[1], _cast_bits_to_array_expr_flattened[1]
             connect _cast_bits_to_array_expr_flattened[2], bits(bits(bits(i2, 9, 2), 2, 0), 2, 2)
             connect _cast_bits_to_array_expr[2], _cast_bits_to_array_expr_flattened[2]
+            ; connect different types:
+            ; lhs: UInt<8>
+            ; rhs: UInt<1>
             connect o[2], _cast_bits_to_array_expr[1] @[module-XXXXXXXXXX.rs 16:1]
         when eq(bits(i2, 1, 0), UInt<2>(0h0)): @[module-XXXXXXXXXX.rs 17:1]
             connect o[3], UInt<8>(0h0) @[module-XXXXXXXXXX.rs 18:1]
@@ -945,6 +978,9 @@ circuit check_struct_enum_match:
             connect _cast_bits_to_array_expr_1[1], _cast_bits_to_array_expr_flattened_1[1]
             connect _cast_bits_to_array_expr_flattened_1[2], bits(bits(bits(i2, 9, 2), 2, 0), 2, 2)
             connect _cast_bits_to_array_expr_1[2], _cast_bits_to_array_expr_flattened_1[2]
+            ; connect different types:
+            ; lhs: UInt<8>
+            ; rhs: UInt<1>
             connect o[4], _cast_bits_to_array_expr_1[2] @[module-XXXXXXXXXX.rs 24:1]
 ",
     };
@@ -2454,10 +2490,16 @@ circuit check_memory_of_enum: %[[
         connect mem_1.w1.addr, mem_w1.addr @[module-XXXXXXXXXX.rs 14:1]
         connect mem_1.w1.clk, mem_w1.clk @[module-XXXXXXXXXX.rs 14:1]
         connect mem_1.w1.en, mem_w1.en @[module-XXXXXXXXXX.rs 14:1]
+        ; connect different types:
+        ; lhs: UInt<4>
+        ; rhs: UInt<8>
         connect mem_r0.addr, raddr @[module-XXXXXXXXXX.rs 10:1]
         connect mem_r0.en, UInt<1>(0h1) @[module-XXXXXXXXXX.rs 11:1]
         connect mem_r0.clk, clk @[module-XXXXXXXXXX.rs 12:1]
         connect rdata, mem_r0.data @[module-XXXXXXXXXX.rs 13:1]
+        ; connect different types:
+        ; lhs: UInt<4>
+        ; rhs: UInt<8>
         connect mem_w1.addr, waddr @[module-XXXXXXXXXX.rs 15:1]
         connect mem_w1.en, UInt<1>(0h1) @[module-XXXXXXXXXX.rs 16:1]
         connect mem_w1.clk, clk @[module-XXXXXXXXXX.rs 17:1]
@@ -2578,10 +2620,16 @@ circuit check_memory_of_enum: %[[
         connect mem_w1_1.data, mem_w1.data @[module-XXXXXXXXXX.rs 14:1]
         connect mem_w1_1.mask.tag, mem_w1.mask @[module-XXXXXXXXXX.rs 14:1]
         connect mem_w1_1.mask.body, mem_w1.mask @[module-XXXXXXXXXX.rs 14:1]
+        ; connect different types:
+        ; lhs: UInt<4>
+        ; rhs: UInt<8>
         connect mem_r0.addr, raddr @[module-XXXXXXXXXX.rs 10:1]
         connect mem_r0.en, UInt<1>(0h1) @[module-XXXXXXXXXX.rs 11:1]
         connect mem_r0.clk, clk @[module-XXXXXXXXXX.rs 12:1]
         connect rdata, mem_r0.data @[module-XXXXXXXXXX.rs 13:1]
+        ; connect different types:
+        ; lhs: UInt<4>
+        ; rhs: UInt<8>
         connect mem_w1.addr, waddr @[module-XXXXXXXXXX.rs 15:1]
         connect mem_w1.en, UInt<1>(0h1) @[module-XXXXXXXXXX.rs 16:1]
         connect mem_w1.clk, clk @[module-XXXXXXXXXX.rs 17:1]
@@ -2702,10 +2750,16 @@ circuit check_memory_of_enum: %[[
         connect mem_w1_1.data, mem_w1.data @[module-XXXXXXXXXX.rs 14:1]
         connect mem_w1_1.mask.tag, mem_w1.mask @[module-XXXXXXXXXX.rs 14:1]
         connect mem_w1_1.mask.body, mem_w1.mask @[module-XXXXXXXXXX.rs 14:1]
+        ; connect different types:
+        ; lhs: UInt<4>
+        ; rhs: UInt<8>
         connect mem_r0.addr, raddr @[module-XXXXXXXXXX.rs 10:1]
         connect mem_r0.en, UInt<1>(0h1) @[module-XXXXXXXXXX.rs 11:1]
         connect mem_r0.clk, clk @[module-XXXXXXXXXX.rs 12:1]
         connect rdata, mem_r0.data @[module-XXXXXXXXXX.rs 13:1]
+        ; connect different types:
+        ; lhs: UInt<4>
+        ; rhs: UInt<8>
         connect mem_w1.addr, waddr @[module-XXXXXXXXXX.rs 15:1]
         connect mem_w1.en, UInt<1>(0h1) @[module-XXXXXXXXXX.rs 16:1]
         connect mem_w1.clk, clk @[module-XXXXXXXXXX.rs 17:1]
@@ -2778,10 +2832,16 @@ circuit check_memory_of_enum: %[[
             read-under-write => old
             reader => r0
             writer => w1
+        ; connect different types:
+        ; lhs: UInt<4>
+        ; rhs: UInt<8>
         connect `mem`.r0.addr, raddr @[module-XXXXXXXXXX.rs 10:1]
         connect `mem`.r0.en, UInt<1>(0h1) @[module-XXXXXXXXXX.rs 11:1]
         connect `mem`.r0.clk, clk @[module-XXXXXXXXXX.rs 12:1]
         connect rdata, `mem`.r0.data @[module-XXXXXXXXXX.rs 13:1]
+        ; connect different types:
+        ; lhs: UInt<4>
+        ; rhs: UInt<8>
         connect `mem`.w1.addr, waddr @[module-XXXXXXXXXX.rs 15:1]
         connect `mem`.w1.en, UInt<1>(0h1) @[module-XXXXXXXXXX.rs 16:1]
         connect `mem`.w1.clk, clk @[module-XXXXXXXXXX.rs 17:1]
@@ -3284,7 +3344,13 @@ circuit check_enum_connect_any:
         output o1: Ty3 @[module-XXXXXXXXXX.rs 5:1]
         output o2: Ty5 @[module-XXXXXXXXXX.rs 6:1]
         when swap: @[module-XXXXXXXXXX.rs 7:1]
+            ; connect different types:
+            ; lhs: Enum {A(UInt<1>), B(Enum {HdlNone, HdlSome(SInt<1>)}), C(Enum {HdlNone, HdlSome(Bundle {})})}
+            ; rhs: Enum {A(UInt<2>), B(Enum {HdlNone, HdlSome(SInt<2>)}), C(Enum {HdlNone, HdlSome(Bundle {})})}
             connect o1, i2 @[module-XXXXXXXXXX.rs 8:1]
+            ; connect different types:
+            ; lhs: Enum {A(UInt<2>), B(Enum {HdlNone, HdlSome(SInt<2>)}), C(Enum {HdlNone, HdlSome(Bundle {})})}
+            ; rhs: Enum {A(UInt<1>), B(Enum {HdlNone, HdlSome(SInt<1>)}), C(Enum {HdlNone, HdlSome(Bundle {})})}
             connect o2, i1 @[module-XXXXXXXXXX.rs 9:1]
         else:
             connect o1, i1 @[module-XXXXXXXXXX.rs 10:1]
@@ -3323,6 +3389,9 @@ circuit check_enum_connect_any:
             match i2.tag: @[module-XXXXXXXXXX.rs 8:1]
                 A:
                     wire __connect_variant_body: UInt<1> @[module-XXXXXXXXXX.rs 8:1]
+                    ; connect different types:
+                    ; lhs: UInt<1>
+                    ; rhs: UInt<2>
                     connect __connect_variant_body, bits(i2.body, 1, 0) @[module-XXXXXXXXXX.rs 8:1]
                     wire _bundle_literal_expr: Ty1
                     connect _bundle_literal_expr.tag, {|A, B, C|}(A)
@@ -3360,6 +3429,9 @@ circuit check_enum_connect_any:
                             connect _cast_bits_to_bundle_expr_1.tag, _cast_bits_to_enum_expr_1
                             connect _cast_bits_to_bundle_expr_flattened_1.body, bits(bits(i2.body, 2, 0), 2, 1)
                             connect _cast_bits_to_bundle_expr_1.body, _cast_bits_to_bundle_expr_flattened_1.body
+                            ; connect different types:
+                            ; lhs: SInt<1>
+                            ; rhs: SInt<2>
                             connect __connect_variant_body_2, asSInt(bits(_cast_bits_to_bundle_expr_1.body, 1, 0)) @[module-XXXXXXXXXX.rs 8:1]
                             wire _bundle_literal_expr_2: Ty4
                             connect _bundle_literal_expr_2.tag, {|HdlNone, HdlSome|}(HdlSome)
@@ -3412,6 +3484,9 @@ circuit check_enum_connect_any:
             match i1.tag: @[module-XXXXXXXXXX.rs 9:1]
                 A:
                     wire __connect_variant_body_4: UInt<2> @[module-XXXXXXXXXX.rs 9:1]
+                    ; connect different types:
+                    ; lhs: UInt<2>
+                    ; rhs: UInt<1>
                     connect __connect_variant_body_4, bits(i1.body, 0, 0) @[module-XXXXXXXXXX.rs 9:1]
                     wire _bundle_literal_expr_5: Ty2
                     connect _bundle_literal_expr_5.tag, {|A, B, C|}(A)
@@ -3449,6 +3524,9 @@ circuit check_enum_connect_any:
                             connect _cast_bits_to_bundle_expr_4.tag, _cast_bits_to_enum_expr_4
                             connect _cast_bits_to_bundle_expr_flattened_4.body, bits(bits(i1.body, 1, 0), 1, 1)
                             connect _cast_bits_to_bundle_expr_4.body, _cast_bits_to_bundle_expr_flattened_4.body
+                            ; connect different types:
+                            ; lhs: SInt<2>
+                            ; rhs: SInt<1>
                             connect __connect_variant_body_6, asSInt(bits(_cast_bits_to_bundle_expr_4.body, 0, 0)) @[module-XXXXXXXXXX.rs 9:1]
                             wire _bundle_literal_expr_7: Ty5
                             connect _bundle_literal_expr_7.tag, {|HdlNone, HdlSome|}(HdlSome)
@@ -3524,6 +3602,9 @@ circuit check_enum_connect_any:
         when swap: @[module-XXXXXXXXXX.rs 7:1]
             when eq(i2.tag, UInt<2>(0h0)): @[module-XXXXXXXXXX.rs 8:1]
                 wire __connect_variant_body: UInt<1> @[module-XXXXXXXXXX.rs 8:1]
+                ; connect different types:
+                ; lhs: UInt<1>
+                ; rhs: UInt<2>
                 connect __connect_variant_body, bits(i2.body, 1, 0) @[module-XXXXXXXXXX.rs 8:1]
                 wire _bundle_literal_expr: Ty0
                 connect _bundle_literal_expr.tag, UInt<2>(0h0)
@@ -3550,6 +3631,9 @@ circuit check_enum_connect_any:
                     connect _cast_bits_to_bundle_expr_1.tag, _cast_bits_to_bundle_expr_flattened_1.tag
                     connect _cast_bits_to_bundle_expr_flattened_1.body, bits(bits(i2.body, 2, 0), 2, 1)
                     connect _cast_bits_to_bundle_expr_1.body, _cast_bits_to_bundle_expr_flattened_1.body
+                    ; connect different types:
+                    ; lhs: SInt<1>
+                    ; rhs: SInt<2>
                     connect __connect_variant_body_2, asSInt(bits(_cast_bits_to_bundle_expr_1.body, 1, 0)) @[module-XXXXXXXXXX.rs 8:1]
                     wire _bundle_literal_expr_2: Ty2
                     connect _bundle_literal_expr_2.tag, UInt<1>(0h1)
@@ -3584,6 +3668,9 @@ circuit check_enum_connect_any:
                 connect o1, _bundle_literal_expr_4 @[module-XXXXXXXXXX.rs 8:1]
             when eq(i1.tag, UInt<2>(0h0)): @[module-XXXXXXXXXX.rs 9:1]
                 wire __connect_variant_body_4: UInt<2> @[module-XXXXXXXXXX.rs 9:1]
+                ; connect different types:
+                ; lhs: UInt<2>
+                ; rhs: UInt<1>
                 connect __connect_variant_body_4, bits(i1.body, 0, 0) @[module-XXXXXXXXXX.rs 9:1]
                 wire _bundle_literal_expr_5: Ty1
                 connect _bundle_literal_expr_5.tag, UInt<2>(0h0)
@@ -3610,6 +3697,9 @@ circuit check_enum_connect_any:
                     connect _cast_bits_to_bundle_expr_4.tag, _cast_bits_to_bundle_expr_flattened_4.tag
                     connect _cast_bits_to_bundle_expr_flattened_4.body, bits(bits(i1.body, 1, 0), 1, 1)
                     connect _cast_bits_to_bundle_expr_4.body, _cast_bits_to_bundle_expr_flattened_4.body
+                    ; connect different types:
+                    ; lhs: SInt<2>
+                    ; rhs: SInt<1>
                     connect __connect_variant_body_6, asSInt(bits(_cast_bits_to_bundle_expr_4.body, 0, 0)) @[module-XXXXXXXXXX.rs 9:1]
                     wire _bundle_literal_expr_7: Ty3
                     connect _bundle_literal_expr_7.tag, UInt<1>(0h1)
@@ -3667,6 +3757,9 @@ circuit check_enum_connect_any:
         when swap: @[module-XXXXXXXXXX.rs 7:1]
             when eq(bits(i2, 1, 0), UInt<2>(0h0)): @[module-XXXXXXXXXX.rs 8:1]
                 wire __connect_variant_body: UInt<1> @[module-XXXXXXXXXX.rs 8:1]
+                ; connect different types:
+                ; lhs: UInt<1>
+                ; rhs: UInt<2>
                 connect __connect_variant_body, bits(bits(i2, 4, 2), 1, 0) @[module-XXXXXXXXXX.rs 8:1]
                 wire _bundle_literal_expr: Ty0
                 connect _bundle_literal_expr.tag, UInt<2>(0h0)
@@ -3691,6 +3784,9 @@ circuit check_enum_connect_any:
                     connect __connect_variant_body_1, _cast_to_bits_expr_1 @[module-XXXXXXXXXX.rs 8:1]
                 else:
                     wire __connect_variant_body_2: SInt<1> @[module-XXXXXXXXXX.rs 8:1]
+                    ; connect different types:
+                    ; lhs: SInt<1>
+                    ; rhs: SInt<2>
                     connect __connect_variant_body_2, asSInt(bits(bits(bits(bits(i2, 4, 2), 2, 0), 2, 1), 1, 0)) @[module-XXXXXXXXXX.rs 8:1]
                     wire _bundle_literal_expr_2: Ty1
                     connect _bundle_literal_expr_2.tag, UInt<1>(0h1)
@@ -3724,6 +3820,9 @@ circuit check_enum_connect_any:
                 connect o1, _cast_to_bits_expr_4 @[module-XXXXXXXXXX.rs 8:1]
             when eq(bits(i1, 1, 0), UInt<2>(0h0)): @[module-XXXXXXXXXX.rs 9:1]
                 wire __connect_variant_body_4: UInt<2> @[module-XXXXXXXXXX.rs 9:1]
+                ; connect different types:
+                ; lhs: UInt<2>
+                ; rhs: UInt<1>
                 connect __connect_variant_body_4, bits(bits(i1, 3, 2), 0, 0) @[module-XXXXXXXXXX.rs 9:1]
                 wire _bundle_literal_expr_5: Ty2
                 connect _bundle_literal_expr_5.tag, UInt<2>(0h0)
@@ -3748,6 +3847,9 @@ circuit check_enum_connect_any:
                     connect __connect_variant_body_5, _cast_to_bits_expr_6 @[module-XXXXXXXXXX.rs 9:1]
                 else:
                     wire __connect_variant_body_6: SInt<2> @[module-XXXXXXXXXX.rs 9:1]
+                    ; connect different types:
+                    ; lhs: SInt<2>
+                    ; rhs: SInt<1>
                     connect __connect_variant_body_6, asSInt(bits(bits(bits(bits(i1, 3, 2), 1, 0), 1, 1), 0, 0)) @[module-XXXXXXXXXX.rs 9:1]
                     wire _bundle_literal_expr_7: Ty3
                     connect _bundle_literal_expr_7.tag, UInt<1>(0h1)