diff --git a/lib/pb/serializable.rb b/lib/pb/serializable.rb
index fdb0b22..327b4e7 100644
--- a/lib/pb/serializable.rb
+++ b/lib/pb/serializable.rb
@@ -17,7 +17,7 @@ def self.included(base)
     # @param with [
     #   Google::Protobuf::FieldMask,
     #   Array<(Symbol, Hash)>,
-    #   Hash{Symbol=>(Array,Symbol,Hash)},
+    #   Hash{Symbol=>(Array,Symbol,Hash,Proc)},
     #   ]
     #   Specifies the list of fields to be serialized in the Proto message object.
     #   `nil` means that all fields defined in .proto will be serialized.
diff --git a/lib/pb/serializer.rb b/lib/pb/serializer.rb
index 9c8aadd..f8c97e7 100644
--- a/lib/pb/serializer.rb
+++ b/lib/pb/serializer.rb
@@ -81,7 +81,7 @@ def build_default_mask(descriptor)
                 "google.protobuf.BoolValue"  ,
                 "google.protobuf.BytesValue" then m << fd.name.to_sym
               else
-                m << { fd.name.to_sym => build_default_mask(fd.subtype) }
+                m << { fd.name.to_sym => -> { build_default_mask(fd.subtype) } }
               end
             else
               m << fd.name.to_sym
@@ -102,22 +102,24 @@ def parse_field_mask(field_mask)
         end
       end
 
-      # @param input [Google::Protobuf::FieldMask, Symbol, Array<(Symbol,Hash)>, Hash{Symbol=>(Array,Symbol,Hash)}]
-      # @return [Hash{Symbol=>(Array,Hash)}]
+      # @param input [Google::Protobuf::FieldMask, Symbol, Array<(Symbol,Hash)>, Hash{Symbol=>(Array,Symbol,Hash,Proc)}, Proc]
+      # @return [Hash{Symbol=>(Array,Hash,Proc)}]
       def normalize_mask(input)
         if input.kind_of?(Google::Protobuf::FieldMask)
           input = parse_field_mask(input)
         end
 
-        normalized = {}
-
+        input = input.call if input.kind_of?(Proc)
         input = [input] if input.kind_of?(Hash)
+
+        normalized = {}
         Array(input).each do |el|
           case el
           when Symbol
             normalized[el] ||= []
           when Hash
             el.each do |k, v|
+              v = v.call if v.kind_of?(Proc)
               v = [v] if v.kind_of?(Hash)
               normalized[k] ||= []
               normalized[k].push(*Array(v))
diff --git a/spec/examples/recursive_spec.rb b/spec/examples/recursive_spec.rb
new file mode 100644
index 0000000..04c5ce1
--- /dev/null
+++ b/spec/examples/recursive_spec.rb
@@ -0,0 +1,33 @@
+RSpec.describe 'recursive models' do
+  module self::Sandbox
+    class StringListSerializer < Pb::Serializer::Base
+      message TestFixture::Recursive::StringList
+
+      attribute :car
+      attribute :cdr, allow_nil: true, serializer: StringListSerializer
+    end
+
+    StringList = Struct.new(:car, :cdr)
+  end
+
+  let(:sandbox) { self.class::Sandbox }
+
+  it "serializes recursive ruby object into protobuf type" do
+    l = sandbox::StringList.new(
+      "Alpha",
+      sandbox::StringList.new(
+        "Bravo",
+        sandbox::StringList.new(
+          "Charlie",
+          nil,
+        ),
+      ),
+    )
+    pb = sandbox::StringListSerializer.new(l).to_pb
+
+    expect(pb).to be_a(TestFixture::Recursive::StringList)
+    expect(pb.car).to eq "Alpha"
+    expect(pb.cdr.car).to eq "Bravo"
+    expect(pb.cdr.cdr.car).to eq "Charlie"
+  end
+end
diff --git a/spec/fixtures/recursive_model.proto b/spec/fixtures/recursive_model.proto
new file mode 100644
index 0000000..4e877c3
--- /dev/null
+++ b/spec/fixtures/recursive_model.proto
@@ -0,0 +1,10 @@
+syntax = "proto3";
+
+package example.recursive;
+
+option ruby_package = "TestFixture::Recursive";
+
+message StringList {
+  string car = 1;
+  StringList cdr = 2;
+}
diff --git a/spec/fixtures/recursive_model_pb.rb b/spec/fixtures/recursive_model_pb.rb
new file mode 100644
index 0000000..68cb3fd
--- /dev/null
+++ b/spec/fixtures/recursive_model_pb.rb
@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+# Generated by the protocol buffer compiler.  DO NOT EDIT!
+# source: recursive_model.proto
+
+require 'google/protobuf'
+
+
+descriptor_data = "\n\x15recursive_model.proto\x12\x11\x65xample.recursive\"E\n\nStringList\x12\x0b\n\x03\x63\x61r\x18\x01 \x01(\t\x12*\n\x03\x63\x64r\x18\x02 \x01(\x0b\x32\x1d.example.recursive.StringListB\x19\xea\x02\x16TestFixture::Recursiveb\x06proto3"
+
+pool = Google::Protobuf::DescriptorPool.generated_pool
+
+begin
+  pool.add_serialized_file(descriptor_data)
+rescue TypeError => e
+  # Compatibility code: will be removed in the next major version.
+  require 'google/protobuf/descriptor_pb'
+  parsed = Google::Protobuf::FileDescriptorProto.decode(descriptor_data)
+  parsed.clear_dependency
+  serialized = parsed.class.encode(parsed)
+  file = pool.add_serialized_file(serialized)
+  warn "Warning: Protobuf detected an import path issue while loading generated file #{__FILE__}"
+  imports = [
+  ]
+  imports.each do |type_name, expected_filename|
+    import_file = pool.lookup(type_name).file_descriptor
+    if import_file.name != expected_filename
+      warn "- #{file.name} imports #{expected_filename}, but that import was loaded as #{import_file.name}"
+    end
+  end
+  warn "Each proto file must use a consistent fully-qualified name."
+  warn "This will become an error in the next major version."
+end
+
+module TestFixture
+  module Recursive
+    StringList = ::Google::Protobuf::DescriptorPool.generated_pool.lookup("example.recursive.StringList").msgclass
+  end
+end