diff --git a/src/http/middleware.zig b/src/http/middleware.zig
index 190a60d..541ca97 100644
--- a/src/http/middleware.zig
+++ b/src/http/middleware.zig
@@ -163,27 +163,12 @@ test "InjectContextValue" {
         .handle(.{}, .{}, .{ .efgh = @as(usize, 10) }, ExpectContext(.{ .abcd = 5, .efgh = 10 }){});
 }
 
-fn expectDeepEquals(expected: anytype, actual: anytype) !void {
-    const E = @TypeOf(expected);
-    const A = @TypeOf(actual);
-    if (E == void) return std.testing.expect(A == void);
-    try std.testing.expect(std.meta.fields(E).len == std.meta.fields(A).len);
-    inline for (std.meta.fields(E)) |f| {
-        const e = @field(expected, f.name);
-        const a = @field(actual, f.name);
-        if (comptime std.meta.trait.isZigString(f.field_type)) {
-            try std.testing.expectEqualStrings(a, e);
-        } else {
-            try std.testing.expectEqual(a, e);
-        }
-    }
-}
-
 // Helper for testing purposes
 fn ExpectContext(comptime val: anytype) type {
     return struct {
         pub fn handle(_: @This(), _: anytype, _: anytype, ctx: anytype, _: void) !void {
-            try expectDeepEquals(val, ctx);
+            if (@TypeOf(val) == void) return error.TestUnexpectedResult;
+            try util.testing.expectDeepEqual(@as(@TypeOf(ctx), val), ctx);
         }
     };
 }
@@ -485,7 +470,15 @@ pub fn mount(comptime route: []const u8) Mount(route) {
 test "mount" {
     const testCase = struct {
         fn func(comptime base: []const u8, request: []const u8, comptime expected: ?[]const u8) !void {
-            const result = mount(base).handle(.{}, .{}, addField(.{}, "path", request), expectContext(.{ .path = expected orelse "" }));
+            const result = mount(base).handle(
+                .{},
+                .{},
+                addField(.{}, "path", request),
+                expectContext(.{
+                    .path = expected orelse "",
+                    .mounted_at = std.mem.trim(u8, base, "/"),
+                }),
+            );
             try if (expected != null) result else std.testing.expectError(error.RouteMismatch, result);
         }
     }.func;
@@ -590,7 +583,8 @@ test "ParsePathArgs" {
                 expected: @TypeOf(expected),
                 path: []const u8,
                 fn handle(self: @This(), _: anytype, _: anytype, ctx: anytype, _: void) !void {
-                    try expectDeepEquals(self.expected, ctx.args);
+                    if (@TypeOf(expected) == @TypeOf(null)) return error.TestUnexpectedResult;
+                    try util.testing.expectDeepEqual(@as(@TypeOf(ctx.args), self.expected), ctx.args);
                     try std.testing.expectEqualStrings(self.path, ctx.path);
                 }
             }{ .expected = expected, .path = path };
@@ -619,10 +613,10 @@ test "ParsePathArgs" {
     try testCase("/:foo*", struct { foo: []const u8 }, "/", .{ .foo = "/" });
     try testCase("/:foo*", struct { foo: []const u8 }, "", .{ .foo = "" });
 
-    try std.testing.expectError(error.RouteMismatch, testCase("/:id", struct { id: usize }, "/", .{}));
-    try std.testing.expectError(error.RouteMismatch, testCase("/abcd/:id", struct { id: usize }, "/123", .{}));
-    try std.testing.expectError(error.RouteMismatch, testCase("/:id", struct { id: usize }, "/3/id/blahblah", .{ .id = 3 }));
-    try std.testing.expectError(error.InvalidCharacter, testCase("/:id", struct { id: usize }, "/xyz", .{}));
+    try std.testing.expectError(error.RouteMismatch, testCase("/:id", struct { id: usize }, "/", null));
+    try std.testing.expectError(error.RouteMismatch, testCase("/abcd/:id", struct { id: usize }, "/123", null));
+    try std.testing.expectError(error.RouteMismatch, testCase("/:id", struct { id: usize }, "/3/id/blahblah", null));
+    try std.testing.expectError(error.InvalidCharacter, testCase("/:id", struct { id: usize }, "/xyz", null));
 }
 
 const BaseContentType = enum {
@@ -715,7 +709,7 @@ pub fn ParseBody(comptime Body: type, comptime options: ParseBodyOptions) type {
         }
     };
 }
-pub fn parseBody(comptime Body: type) ParseBody(Body) {
+pub fn parseBody(comptime Body: type, comptime options: ParseBodyOptions) ParseBody(Body, options) {
     return .{};
 }
 
@@ -752,7 +746,7 @@ test "parseBody" {
     var headers = http.Fields.init(std.testing.allocator);
     defer headers.deinit();
 
-    try parseBody(Struct).handle(
+    try parseBody(Struct, .{}).handle(
         .{ .body = @as(?std.io.StreamSource, stream), .headers = headers },
         .{},
         .{ .allocator = std.testing.allocator },
diff --git a/src/http/multipart.zig b/src/http/multipart.zig
index 854b7c3..e4c3880 100644
--- a/src/http/multipart.zig
+++ b/src/http/multipart.zig
@@ -357,6 +357,6 @@ test "parseFormData" {
     var src = std.io.StreamSource{ .const_buffer = std.io.fixedBufferStream(body) };
     const val = try parseFormData(struct {
         foo: []const u8,
-    }, "abcd", src.reader(), std.testing.allocator);
+    }, false, "abcd", src.reader(), std.testing.allocator);
     util.deepFree(std.testing.allocator, val);
 }
diff --git a/src/http/urlencode.zig b/src/http/urlencode.zig
index fdfb680..85cc7b9 100644
--- a/src/http/urlencode.zig
+++ b/src/http/urlencode.zig
@@ -252,49 +252,49 @@ fn formatQuery(comptime prefix: []const u8, params: anytype, writer: anytype) !v
 
 test "parse" {
     const testCase = struct {
-        fn case(comptime T: type, expected: T, query_string: []const u8) !void {
-            const result = try parse(std.testing.allocator, T, query_string);
+        fn case(allow_unknown_fields: bool, comptime T: type, expected: T, query_string: []const u8) !void {
+            const result = try parse(std.testing.allocator, allow_unknown_fields, T, query_string);
             defer parseFree(std.testing.allocator, result);
             try util.testing.expectDeepEqual(expected, result);
         }
     }.case;
 
-    try testCase(struct { int: usize = 3 }, .{ .int = 3 }, "");
-    try testCase(struct { int: usize = 3 }, .{ .int = 2 }, "int=2");
-    try testCase(struct { int: usize = 3 }, .{ .int = 2 }, "int=2&");
-    try testCase(struct { boolean: bool = false }, .{ .boolean = false }, "");
-    try testCase(struct { boolean: bool = false }, .{ .boolean = true }, "boolean");
-    try testCase(struct { boolean: bool = false }, .{ .boolean = true }, "boolean=true");
-    try testCase(struct { boolean: bool = false }, .{ .boolean = true }, "boolean=y");
-    try testCase(struct { boolean: bool = false }, .{ .boolean = false }, "boolean=f");
-    try testCase(struct { boolean: bool = false }, .{ .boolean = false }, "boolean=no");
-    try testCase(struct { str_enum: ?enum { foo, bar } = null }, .{ .str_enum = null }, "");
-    try testCase(struct { str_enum: ?enum { foo, bar } = null }, .{ .str_enum = .foo }, "str_enum=foo");
-    try testCase(struct { str_enum: ?enum { foo, bar } = null }, .{ .str_enum = .bar }, "str_enum=bar");
-    try testCase(struct { str_enum: ?enum { foo, bar } = .foo }, .{ .str_enum = .foo }, "");
-    try testCase(struct { str_enum: ?enum { foo, bar } = .foo }, .{ .str_enum = null }, "str_enum");
-    try testCase(struct { n1: usize = 5, n2: usize = 5 }, .{ .n1 = 1, .n2 = 2 }, "n1=1&n2=2");
-    try testCase(struct { n1: usize = 5, n2: usize = 5 }, .{ .n1 = 1, .n2 = 2 }, "n1=1&n2=2&");
-    try testCase(struct { n1: usize = 5, n2: usize = 5 }, .{ .n1 = 1, .n2 = 2 }, "n1=1&&n2=2&");
+    try testCase(false, struct { int: usize = 3 }, .{ .int = 3 }, "");
+    try testCase(false, struct { int: usize = 3 }, .{ .int = 2 }, "int=2");
+    try testCase(false, struct { int: usize = 3 }, .{ .int = 2 }, "int=2&");
+    try testCase(false, struct { boolean: bool = false }, .{ .boolean = false }, "");
+    try testCase(false, struct { boolean: bool = false }, .{ .boolean = true }, "boolean");
+    try testCase(false, struct { boolean: bool = false }, .{ .boolean = true }, "boolean=true");
+    try testCase(false, struct { boolean: bool = false }, .{ .boolean = true }, "boolean=y");
+    try testCase(false, struct { boolean: bool = false }, .{ .boolean = false }, "boolean=f");
+    try testCase(false, struct { boolean: bool = false }, .{ .boolean = false }, "boolean=no");
+    try testCase(false, struct { str_enum: ?enum { foo, bar } = null }, .{ .str_enum = null }, "");
+    try testCase(false, struct { str_enum: ?enum { foo, bar } = null }, .{ .str_enum = .foo }, "str_enum=foo");
+    try testCase(false, struct { str_enum: ?enum { foo, bar } = null }, .{ .str_enum = .bar }, "str_enum=bar");
+    try testCase(false, struct { str_enum: ?enum { foo, bar } = .foo }, .{ .str_enum = .foo }, "");
+    try testCase(false, struct { str_enum: ?enum { foo, bar } = .foo }, .{ .str_enum = null }, "str_enum");
+    try testCase(false, struct { n1: usize = 5, n2: usize = 5 }, .{ .n1 = 1, .n2 = 2 }, "n1=1&n2=2");
+    try testCase(false, struct { n1: usize = 5, n2: usize = 5 }, .{ .n1 = 1, .n2 = 2 }, "n1=1&n2=2&");
+    try testCase(false, struct { n1: usize = 5, n2: usize = 5 }, .{ .n1 = 1, .n2 = 2 }, "n1=1&&n2=2&");
 
-    try testCase(struct { str: ?[]const u8 = null }, .{ .str = null }, "");
-    try testCase(struct { str: ?[]const u8 = null }, .{ .str = null }, "str");
-    try testCase(struct { str: ?[]const u8 = null }, .{ .str = null }, "str=");
-    try testCase(struct { str: ?[]const u8 = null }, .{ .str = "foo" }, "str=foo");
-    try testCase(struct { str: ?[]const u8 = "foo" }, .{ .str = "foo" }, "str=foo");
-    try testCase(struct { str: ?[]const u8 = "foo" }, .{ .str = "foo" }, "");
-    try testCase(struct { str: ?[]const u8 = "foo" }, .{ .str = null }, "str");
-    try testCase(struct { str: ?[]const u8 = "foo" }, .{ .str = null }, "str=");
+    try testCase(false, struct { str: ?[]const u8 = null }, .{ .str = null }, "");
+    try testCase(false, struct { str: ?[]const u8 = null }, .{ .str = null }, "str");
+    try testCase(false, struct { str: ?[]const u8 = null }, .{ .str = null }, "str=");
+    try testCase(false, struct { str: ?[]const u8 = null }, .{ .str = "foo" }, "str=foo");
+    try testCase(false, struct { str: ?[]const u8 = "foo" }, .{ .str = "foo" }, "str=foo");
+    try testCase(false, struct { str: ?[]const u8 = "foo" }, .{ .str = "foo" }, "");
+    try testCase(false, struct { str: ?[]const u8 = "foo" }, .{ .str = null }, "str");
+    try testCase(false, struct { str: ?[]const u8 = "foo" }, .{ .str = null }, "str=");
 
     const rand_uuid = comptime util.Uuid.parse("c1fb6578-4d0c-4eb9-9f67-d56da3ae6f5d") catch unreachable;
-    try testCase(struct { id: ?util.Uuid = null }, .{ .id = null }, "");
-    try testCase(struct { id: ?util.Uuid = null }, .{ .id = null }, "id=");
-    try testCase(struct { id: ?util.Uuid = null }, .{ .id = null }, "id");
-    try testCase(struct { id: ?util.Uuid = null }, .{ .id = rand_uuid }, "id=" ++ rand_uuid.toCharArray());
-    try testCase(struct { id: ?util.Uuid = rand_uuid }, .{ .id = rand_uuid }, "");
-    try testCase(struct { id: ?util.Uuid = rand_uuid }, .{ .id = null }, "id=");
-    try testCase(struct { id: ?util.Uuid = rand_uuid }, .{ .id = null }, "id");
-    try testCase(struct { id: ?util.Uuid = rand_uuid }, .{ .id = rand_uuid }, "id=" ++ rand_uuid.toCharArray());
+    try testCase(false, struct { id: ?util.Uuid = null }, .{ .id = null }, "");
+    try testCase(false, struct { id: ?util.Uuid = null }, .{ .id = null }, "id=");
+    try testCase(false, struct { id: ?util.Uuid = null }, .{ .id = null }, "id");
+    try testCase(false, struct { id: ?util.Uuid = null }, .{ .id = rand_uuid }, "id=" ++ rand_uuid.toCharArray());
+    try testCase(false, struct { id: ?util.Uuid = rand_uuid }, .{ .id = rand_uuid }, "");
+    try testCase(false, struct { id: ?util.Uuid = rand_uuid }, .{ .id = null }, "id=");
+    try testCase(false, struct { id: ?util.Uuid = rand_uuid }, .{ .id = null }, "id");
+    try testCase(false, struct { id: ?util.Uuid = rand_uuid }, .{ .id = rand_uuid }, "id=" ++ rand_uuid.toCharArray());
 
     const SubStruct = struct {
         sub: struct {
@@ -302,9 +302,9 @@ test "parse" {
             bar: usize = 2,
         } = .{},
     };
-    try testCase(SubStruct, .{ .sub = .{ .foo = 1, .bar = 2 } }, "");
-    try testCase(SubStruct, .{ .sub = .{ .foo = 3, .bar = 3 } }, "sub.foo=3&sub.bar=3");
-    try testCase(SubStruct, .{ .sub = .{ .foo = 3, .bar = 2 } }, "sub.foo=3");
+    try testCase(false, SubStruct, .{ .sub = .{ .foo = 1, .bar = 2 } }, "");
+    try testCase(false, SubStruct, .{ .sub = .{ .foo = 3, .bar = 3 } }, "sub.foo=3&sub.bar=3");
+    try testCase(false, SubStruct, .{ .sub = .{ .foo = 3, .bar = 2 } }, "sub.foo=3");
 
     // TODO: Semantics are ill-defined here. What happens if the substruct doesn't have
     // default values?
@@ -313,8 +313,8 @@ test "parse" {
     //         foo: usize = 1,
     //     } = null,
     // };
-    // try testCase(SubStruct2, .{ .sub = null }, "");
-    // try testCase(SubStruct2, .{ .sub = null }, "sub=");
+    // try testCase(false, SubStruct2, .{ .sub = null }, "");
+    // try testCase(false, SubStruct2, .{ .sub = null }, "sub=");
 
     // TODO: also here (semantics are well defined it just breaks tests)
     // const SubUnion = struct {
@@ -323,21 +323,24 @@ test "parse" {
     //         bar: usize,
     //     } = null,
     // };
-    // try testCase(SubUnion, .{ .sub = null }, "");
-    // try testCase(SubUnion, .{ .sub = null }, "sub=");
+    // try testCase(false, SubUnion, .{ .sub = null }, "");
+    // try testCase(false, SubUnion, .{ .sub = null }, "sub=");
 
     const SubUnion2 = struct {
-        sub: ?struct {
-            foo: usize,
-            val: union(enum) {
+        sub: ?union(enum) {
+            bar: struct {
+                foo: usize,
                 bar: []const u8,
+            },
+            baz: struct {
+                foo: usize,
                 baz: []const u8,
             },
         } = null,
     };
-    try testCase(SubUnion2, .{ .sub = null }, "");
-    try testCase(SubUnion2, .{ .sub = .{ .foo = 1, .val = .{ .bar = "abc" } } }, "sub.foo=1&sub.bar=abc");
-    try testCase(SubUnion2, .{ .sub = .{ .foo = 1, .val = .{ .baz = "abc" } } }, "sub.foo=1&sub.baz=abc");
+    try testCase(false, SubUnion2, .{ .sub = null }, "");
+    try testCase(false, SubUnion2, .{ .sub = .{ .bar = .{ .foo = 1, .bar = "abc" } } }, "sub.foo=1&sub.bar=abc");
+    try testCase(false, SubUnion2, .{ .sub = .{ .baz = .{ .foo = 1, .baz = "abc" } } }, "sub.foo=1&sub.baz=abc");
 }
 
 test "encodeStruct" {
diff --git a/src/template/lib.zig b/src/template/lib.zig
index 4698cab..2b98606 100644
--- a/src/template/lib.zig
+++ b/src/template/lib.zig
@@ -1349,7 +1349,7 @@ test "template" {
 
     try testCase("", .{}, "");
     try testCase("abcd", .{}, "abcd");
-    try testCase("{.val}", .{ .val = 3 }, "3");
+    try testCase("{.val}", .{ .val = @as(usize, 3) }, "3");
     try testCase("{#if .val}1{/if}", .{ .val = true }, "1");
     try testCase("{#for .vals |$v|=}       {$v}    {=/for}", .{ .vals = [_]u8{ 1, 2, 3 } }, "123");
     try testCase("{#for .vals |$val|}{$val}{/for}", .{ .vals = [_]u8{ 1, 2, 3 } }, "123");
diff --git a/src/util/serialize.zig b/src/util/serialize.zig
index 120ca48..4098688 100644
--- a/src/util/serialize.zig
+++ b/src/util/serialize.zig
@@ -266,7 +266,7 @@ pub fn DeserializerContext(comptime Result: type, comptime From: type, comptime
         }
 
         pub fn finish(self: *@This(), allocator: std.mem.Allocator) !Result {
-            return (try self.deserialize(allocator, Result, self.data, &.{})) orelse
+            return (try self.deserialize(allocator, Result, self.data, &.{}, true)) orelse
                 if (std.meta.fields(Result).len == 0)
                 return .{}
             else
@@ -290,6 +290,7 @@ pub fn DeserializerContext(comptime Result: type, comptime From: type, comptime
             comptime T: type,
             intermediary: anytype,
             comptime field_ref: FieldRef,
+            allow_default: bool,
         ) DeserializeError!?T {
             if (comptime Context.options.isScalar(T)) {
                 const val = @field(intermediary.static, util.comptimeJoin(".", field_ref));
@@ -304,7 +305,7 @@ pub fn DeserializerContext(comptime Result: type, comptime From: type, comptime
                     var partial_match_found: bool = false;
                     inline for (info.fields) |field| {
                         const F = field.field_type;
-                        const maybe_value = self.deserialize(allocator, F, intermediary, field_ref) catch |err| switch (err) {
+                        const maybe_value = self.deserialize(allocator, F, intermediary, field_ref, false) catch |err| switch (err) {
                             error.MissingField => blk: {
                                 partial_match_found = true;
                                 break :blk @as(?F, null);
@@ -333,7 +334,7 @@ pub fn DeserializerContext(comptime Result: type, comptime From: type, comptime
                     inline for (info.fields) |field, i| {
                         const F = field.field_type;
                         const new_field_ref = field_ref ++ &[_][]const u8{field.name};
-                        const maybe_value = try self.deserialize(allocator, F, intermediary, new_field_ref);
+                        const maybe_value = try self.deserialize(allocator, F, intermediary, new_field_ref, false);
                         if (maybe_value) |v| {
                             @field(result, field.name) = v;
                             fields_alloced[i] = true;
@@ -350,7 +351,7 @@ pub fn DeserializerContext(comptime Result: type, comptime From: type, comptime
                     }
                     if (any_missing and any_explicit) return error.MissingField;
 
-                    if (!any_explicit) {
+                    if (!any_explicit and !allow_default) {
                         inline for (info.fields) |field, i| {
                             if (fields_alloced[i]) self.deserializeFree(allocator, @field(result, field.name));
                         }
@@ -369,7 +370,7 @@ pub fn DeserializerContext(comptime Result: type, comptime From: type, comptime
                         var count: usize = 0;
                         errdefer for (result[0..count]) |res| util.deepFree(allocator, res);
                         for (data.items) |sub, i| {
-                            result[i] = (try self.deserialize(allocator, info.child, sub, &.{})) orelse return error.SparseSlice;
+                            result[i] = (try self.deserialize(allocator, info.child, sub, &.{}, false)) orelse return error.SparseSlice;
                         }
 
                         return result;
@@ -378,7 +379,7 @@ pub fn DeserializerContext(comptime Result: type, comptime From: type, comptime
                 },
 
                 // Specifically non-scalar optionals
-                .Optional => |info| return try self.deserialize(allocator, info.child, intermediary, field_ref),
+                .Optional => |info| return try self.deserialize(allocator, info.child, intermediary, field_ref, allow_default),
 
                 else => @compileError("Unsupported type"),
             }
@@ -406,7 +407,8 @@ test "Deserializer" {
     {
         const T = struct { foo: []const u8, bar: bool };
 
-        var ds = Deserializer(T){};
+        var ds = Deserializer(T){ .arena = std.heap.ArenaAllocator.init(std.testing.allocator) };
+        defer ds.deinit();
         try ds.setSerializedField("foo", "123");
         try ds.setSerializedField("bar", "true");
 
@@ -419,7 +421,8 @@ test "Deserializer" {
     {
         const T = struct { foo: []const u8, bar: bool };
 
-        var ds = Deserializer(T){};
+        var ds = Deserializer(T){ .arena = std.heap.ArenaAllocator.init(std.testing.allocator) };
+        defer ds.deinit();
         try std.testing.expectError(error.UnknownField, ds.setSerializedField("baz", "123"));
     }
 
@@ -429,7 +432,8 @@ test "Deserializer" {
             foo: struct { bar: bool, baz: bool },
         };
 
-        var ds = Deserializer(T){};
+        var ds = Deserializer(T){ .arena = std.heap.ArenaAllocator.init(std.testing.allocator) };
+        defer ds.deinit();
         try ds.setSerializedField("foo.bar", "true");
         try ds.setSerializedField("foo.baz", "true");
 
@@ -438,29 +442,45 @@ test "Deserializer" {
         try util.testing.expectDeepEqual(T{ .foo = .{ .bar = true, .baz = true } }, val);
     }
 
-    // Union embedding
+    // Union behavior
     {
         const T = struct {
-            foo: union(enum) { bar: bool, baz: bool },
+            foo: union(enum) {
+                bar: struct {
+                    bar: bool,
+                },
+                baz: struct {
+                    baz: bool,
+                },
+            },
         };
 
-        var ds = Deserializer(T){};
-        try ds.setSerializedField("bar", "true");
+        var ds = Deserializer(T){ .arena = std.heap.ArenaAllocator.init(std.testing.allocator) };
+        defer ds.deinit();
+        try ds.setSerializedField("foo.bar", "true");
 
         const val = try ds.finish(std.testing.allocator);
         defer ds.finishFree(std.testing.allocator, val);
-        try util.testing.expectDeepEqual(T{ .foo = .{ .bar = true } }, val);
+        try util.testing.expectDeepEqual(T{ .foo = .{ .bar = .{ .bar = true } } }, val);
     }
 
     // Returns error if multiple union fields specified
     {
         const T = struct {
-            foo: union(enum) { bar: bool, baz: bool },
+            foo: union(enum) {
+                bar: struct {
+                    bar: bool,
+                },
+                baz: struct {
+                    baz: bool,
+                },
+            },
         };
 
-        var ds = Deserializer(T){};
-        try ds.setSerializedField("bar", "true");
-        try ds.setSerializedField("baz", "true");
+        var ds = Deserializer(T){ .arena = std.heap.ArenaAllocator.init(std.testing.allocator) };
+        defer ds.deinit();
+        try ds.setSerializedField("foo.bar", "true");
+        try ds.setSerializedField("foo.baz", "true");
 
         try std.testing.expectError(error.DuplicateUnionMember, ds.finish(std.testing.allocator));
     }
@@ -469,7 +489,8 @@ test "Deserializer" {
     {
         const T = struct { foo: []const u8 = "123", bar: bool = true };
 
-        var ds = Deserializer(T){};
+        var ds = Deserializer(T){ .arena = std.heap.ArenaAllocator.init(std.testing.allocator) };
+        defer ds.deinit();
 
         const val = try ds.finish(std.testing.allocator);
         defer ds.finishFree(std.testing.allocator, val);
@@ -480,7 +501,8 @@ test "Deserializer" {
     {
         const T = struct { foo: []const u8, bar: bool };
 
-        var ds = Deserializer(T){};
+        var ds = Deserializer(T){ .arena = std.heap.ArenaAllocator.init(std.testing.allocator) };
+        defer ds.deinit();
         try ds.setSerializedField("foo", "123");
 
         try std.testing.expectError(error.MissingField, ds.finish(std.testing.allocator));
@@ -493,7 +515,8 @@ test "Deserializer" {
             qux: ?union(enum) { quux: usize } = null,
         };
 
-        var ds = Deserializer(T){};
+        var ds = Deserializer(T){ .arena = std.heap.ArenaAllocator.init(std.testing.allocator) };
+        defer ds.deinit();
 
         const val = try ds.finish(std.testing.allocator);
         defer ds.finishFree(std.testing.allocator, val);
@@ -506,9 +529,10 @@ test "Deserializer" {
             qux: ?union(enum) { quux: usize } = null,
         };
 
-        var ds = Deserializer(T){};
+        var ds = Deserializer(T){ .arena = std.heap.ArenaAllocator.init(std.testing.allocator) };
+        defer ds.deinit();
         try ds.setSerializedField("foo.baz", "3");
-        try ds.setSerializedField("quux", "3");
+        try ds.setSerializedField("qux", "3");
 
         const val = try ds.finish(std.testing.allocator);
         defer ds.finishFree(std.testing.allocator, val);
@@ -521,9 +545,10 @@ test "Deserializer" {
             qux: ?union(enum) { quux: usize } = null,
         };
 
-        var ds = Deserializer(T){};
+        var ds = Deserializer(T){ .arena = std.heap.ArenaAllocator.init(std.testing.allocator) };
+        defer ds.deinit();
         try ds.setSerializedField("foo.bar", "3");
-        try ds.setSerializedField("quux", "3");
+        try ds.setSerializedField("qux", "3");
 
         try std.testing.expectError(error.MissingField, ds.finish(std.testing.allocator));
     }