diff --git a/src/arch/wasm/CodeGen.zig b/src/arch/wasm/CodeGen.zig
index 4514311160..74eb075eab 100644
--- a/src/arch/wasm/CodeGen.zig
+++ b/src/arch/wasm/CodeGen.zig
@@ -1716,7 +1716,14 @@ fn isByRef(ty: Type, target: std.Target) bool {
         .Array,
         .Frame,
         .Union,
-        => return ty.hasRuntimeBitsIgnoreComptime(),
+        => {
+            if (ty.castTag(.@"union")) |union_ty| {
+                if (union_ty.data.layout == .Packed) {
+                    return ty.abiSize(target) > 8;
+                }
+            }
+            return ty.hasRuntimeBitsIgnoreComptime();
+        },
         .Struct => {
             if (ty.castTag(.@"struct")) |struct_ty| {
                 const struct_obj = struct_ty.data;
@@ -3131,6 +3138,14 @@ fn lowerConstant(func: *CodeGen, arg_val: Value, ty: Type) InnerError!WValue {
             val.writeToMemory(ty, func.bin_file.base.options.module.?, &buf) catch unreachable;
             return func.storeSimdImmd(buf);
         },
+        .Union => {
+            // in this case we have a packed union which will not be passed by reference.
+            const union_ty = ty.cast(Type.Payload.Union).?.data;
+            const union_obj = val.castTag(.@"union").?.data;
+            const field_index = ty.unionTagFieldIndex(union_obj.tag, func.bin_file.base.options.module.?).?;
+            const field_ty = union_ty.fields.values()[field_index].ty;
+            return func.lowerConstant(union_obj.val, field_ty);
+        },
         else => |zig_type| return func.fail("Wasm TODO: LowerConstant for zigTypeTag {}", .{zig_type}),
     }
 }
@@ -3661,8 +3676,42 @@ fn airStructFieldVal(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
                 break :result try truncated.toLocal(func, field_ty);
             },
             .Union => result: {
-                const val = try func.load(operand, field_ty, 0);
-                break :result try val.toLocal(func, field_ty);
+                if (isByRef(struct_ty, func.target)) {
+                    if (!isByRef(field_ty, func.target)) {
+                        const val = try func.load(operand, field_ty, 0);
+                        break :result try val.toLocal(func, field_ty);
+                    } else {
+                        const new_stack_val = try func.allocStack(field_ty);
+                        try func.store(new_stack_val, operand, field_ty, 0);
+                        break :result new_stack_val;
+                    }
+                }
+
+                var payload: Type.Payload.Bits = .{
+                    .base = .{ .tag = .int_unsigned },
+                    .data = @intCast(u16, struct_ty.bitSize(func.target)),
+                };
+                const union_int_type = Type.initPayload(&payload.base);
+                if (field_ty.zigTypeTag() == .Float) {
+                    var int_payload: Type.Payload.Bits = .{
+                        .base = .{ .tag = .int_unsigned },
+                        .data = @intCast(u16, field_ty.bitSize(func.target)),
+                    };
+                    const int_type = Type.initPayload(&int_payload.base);
+                    const truncated = try func.trunc(operand, int_type, union_int_type);
+                    const bitcasted = try func.bitcast(field_ty, int_type, truncated);
+                    break :result try bitcasted.toLocal(func, field_ty);
+                } else if (field_ty.isPtrAtRuntime()) {
+                    var int_payload: Type.Payload.Bits = .{
+                        .base = .{ .tag = .int_unsigned },
+                        .data = @intCast(u16, field_ty.bitSize(func.target)),
+                    };
+                    const int_type = Type.initPayload(&int_payload.base);
+                    const truncated = try func.trunc(operand, int_type, union_int_type);
+                    break :result try truncated.toLocal(func, field_ty);
+                }
+                const truncated = try func.trunc(operand, field_ty, union_int_type);
+                break :result try truncated.toLocal(func, field_ty);
             },
             else => unreachable,
         },