diff --git a/src/language_server_api.cc b/src/language_server_api.cc
index dc9c4357..00c88a23 100644
--- a/src/language_server_api.cc
+++ b/src/language_server_api.cc
@@ -155,7 +155,13 @@ std::unique_ptr<BaseIpcMessage> MessageRegistry::Parse(Reader& visitor) {
   }
 
   Allocator& allocator = allocators[method];
-  return allocator(visitor);
+  // FIXME Print error message for deserialization error
+  try {
+    return allocator(visitor);
+  } catch (std::invalid_argument& e) {
+    LOG_S(ERROR) << "Unable to deserialize request '" << method << "'";
+    return nullptr;
+  }
 }
 
 MessageRegistry* MessageRegistry::instance() {
diff --git a/src/messages/initialize.cc b/src/messages/initialize.cc
index 611d5ec6..e829d527 100644
--- a/src/messages/initialize.cc
+++ b/src/messages/initialize.cc
@@ -10,7 +10,7 @@
 
 #include <loguru.hpp>
 
-#include <iostream>
+#include <stdexcept>
 
 // TODO Cleanup global variables
 extern std::string g_init_options;
@@ -71,7 +71,18 @@ struct InitializeHandler : BaseMessageHandler<Ipc_InitializeRequest> {
         reader.Parse(g_init_options.c_str());
         if (!reader.HasParseError()) {
           JsonReader json_reader{&reader};
-          Reflect(json_reader, *config);
+          try {
+            Reflect(json_reader, *config);
+          } catch (std::invalid_argument& ex) {
+            // FIXME This is not triggered. Need to pass error from
+            // MessageRegistry::Parse in language_server_api.cc
+            Out_ShowLogMessage out;
+            out.display_type = Out_ShowLogMessage::DisplayType::Show;
+            out.params.type = lsMessageType::Error;
+            out.params.message = "Failed to deserialize " +
+                                 json_reader.GetPath() + " " + ex.what();
+            out.Write(std::cout);
+          }
         }
       }
       g_enable_comments = config->enableComments;
diff --git a/src/serializer.cc b/src/serializer.cc
index 25b75154..99ec54b6 100644
--- a/src/serializer.cc
+++ b/src/serializer.cc
@@ -8,6 +8,8 @@
 #include <doctest/doctest.h>
 #include <loguru.hpp>
 
+#include <stdexcept>
+
 namespace {
 bool gTestOutputMode = false;
 }  // namespace
@@ -15,6 +17,7 @@ bool gTestOutputMode = false;
 //// Elementary types
 
 void Reflect(Reader& visitor, uint8_t& value) {
+  if (!visitor.IsInt()) throw std::invalid_argument("uint8_t");
   value = (uint8_t)visitor.GetInt();
 }
 void Reflect(Writer& visitor, uint8_t& value) {
@@ -22,6 +25,7 @@ void Reflect(Writer& visitor, uint8_t& value) {
 }
 
 void Reflect(Reader& visitor, int16_t& value) {
+  if (!visitor.IsInt()) throw std::invalid_argument("int16_t");
   value = (int16_t)visitor.GetInt();
 }
 void Reflect(Writer& visitor, int16_t& value) {
@@ -29,6 +33,7 @@ void Reflect(Writer& visitor, int16_t& value) {
 }
 
 void Reflect(Reader& visitor, int& value) {
+  if (!visitor.IsInt()) throw std::invalid_argument("int");
   value = visitor.GetInt();
 }
 void Reflect(Writer& visitor, int& value) {
@@ -36,6 +41,7 @@ void Reflect(Writer& visitor, int& value) {
 }
 
 void Reflect(Reader& visitor, unsigned& value) {
+  if (!visitor.IsInt()) throw std::invalid_argument("unsigned");
   value = visitor.GetUint32();
 }
 void Reflect(Writer& visitor, unsigned& value) {
@@ -43,6 +49,7 @@ void Reflect(Writer& visitor, unsigned& value) {
 }
 
 void Reflect(Reader& visitor, long& value) {
+  if (!visitor.IsInt64()) throw std::invalid_argument("long");
   value = long(visitor.GetInt64());
 }
 void Reflect(Writer& visitor, long& value) {
@@ -50,6 +57,7 @@ void Reflect(Writer& visitor, long& value) {
 }
 
 void Reflect(Reader& visitor, unsigned long& value) {
+  if (!visitor.IsUint64()) throw std::invalid_argument("unsigned long");
   value = (unsigned long)visitor.GetUint64();
 }
 void Reflect(Writer& visitor, unsigned long& value) {
@@ -57,6 +65,7 @@ void Reflect(Writer& visitor, unsigned long& value) {
 }
 
 void Reflect(Reader& visitor, long long& value) {
+  if (!visitor.IsInt64()) throw std::invalid_argument("long long");
   value = visitor.GetInt64();
 }
 void Reflect(Writer& visitor, long long& value) {
@@ -64,6 +73,7 @@ void Reflect(Writer& visitor, long long& value) {
 }
 
 void Reflect(Reader& visitor, unsigned long long& value) {
+  if (!visitor.IsUint64()) throw std::invalid_argument("unsigned long long");
   value = visitor.GetUint64();
 }
 void Reflect(Writer& visitor, unsigned long long& value) {
@@ -71,6 +81,7 @@ void Reflect(Writer& visitor, unsigned long long& value) {
 }
 
 void Reflect(Reader& visitor, double& value) {
+  if (!visitor.IsDouble()) throw std::invalid_argument("double");
   value = visitor.GetDouble();
 }
 void Reflect(Writer& visitor, double& value) {
@@ -78,6 +89,7 @@ void Reflect(Writer& visitor, double& value) {
 }
 
 void Reflect(Reader& visitor, bool& value) {
+  if (!visitor.IsBool()) throw std::invalid_argument("bool");
   value = visitor.GetBool();
 }
 void Reflect(Writer& visitor, bool& value) {
@@ -86,8 +98,8 @@ void Reflect(Writer& visitor, bool& value) {
 
 // std::string
 void Reflect(Reader& visitor, std::string& value) {
-  if (visitor.IsString())
-    value = visitor.GetString();
+  if (!visitor.IsString()) throw std::invalid_argument("std::string");
+  value = visitor.GetString();
 }
 void Reflect(Writer& visitor, std::string& value) {
   visitor.String(value.c_str(), (rapidjson::SizeType)value.size());
@@ -289,7 +301,14 @@ std::unique_ptr<IndexFile> Deserialize(SerializeFormat format,
 
       file = MakeUnique<IndexFile>(path, nullopt);
       JsonReader json_reader{&reader};
-      Reflect(json_reader, *file);
+      try {
+        Reflect(json_reader, *file);
+      } catch (std::invalid_argument& e) {
+        LOG_S(ERROR) << "'" << path << "': failed to deserialize "
+                     << json_reader.GetPath() << "."
+                     << e.what();
+        return nullptr;
+      }
       break;
     }
 
diff --git a/src/serializer.h b/src/serializer.h
index 10aedea5..c71c6ae4 100644
--- a/src/serializer.h
+++ b/src/serializer.h
@@ -19,12 +19,13 @@ class Reader {
   virtual ~Reader() {}
   virtual SerializeFormat Format() const = 0;
 
-  // virtual bool IsBool() = 0;
+  virtual bool IsBool() = 0;
   virtual bool IsNull() = 0;
   virtual bool IsArray() = 0;
   virtual bool IsInt() = 0;
   virtual bool IsInt64() = 0;
-  // virtual bool IsUint64() = 0;
+  virtual bool IsUint64() = 0;
+  virtual bool IsDouble() = 0;
   virtual bool IsString() = 0;
 
   virtual void GetNull() = 0;
diff --git a/src/serializers/json.h b/src/serializers/json.h
index 67cb53b0..7e766a15 100644
--- a/src/serializers/json.h
+++ b/src/serializers/json.h
@@ -7,17 +7,19 @@
 
 class JsonReader : public Reader {
   rapidjson::GenericValue<rapidjson::UTF8<>>* m_;
+  std::vector<const char*> path_;
 
  public:
   JsonReader(rapidjson::GenericValue<rapidjson::UTF8<>>* m) : m_(m) {}
   SerializeFormat Format() const override { return SerializeFormat::Json; }
 
-  // bool IsBool() override { return m_->IsBool(); }
+  bool IsBool() override { return m_->IsBool(); }
   bool IsNull() override { return m_->IsNull(); }
   bool IsArray() override { return m_->IsArray(); }
   bool IsInt() override { return m_->IsInt(); }
   bool IsInt64() override { return m_->IsInt64(); }
-  // bool IsUint64() override { return m_->IsUint64(); }
+  bool IsUint64() override { return m_->IsUint64(); }
+  bool IsDouble() override { return m_->IsDouble(); }
   bool IsString() override { return m_->IsString(); }
 
   void GetNull() override {}
@@ -36,22 +38,35 @@ class JsonReader : public Reader {
   }
 
   void IterArray(std::function<void(Reader&)> fn) override {
+    if (!m_->IsArray())
+      throw std::invalid_argument("array");
+    // Use "0" to indicate any element for now.
+    path_.push_back("0");
     for (auto& entry : m_->GetArray()) {
       JsonReader sub(&entry);
       fn(sub);
     }
+    path_.pop_back();
   }
 
   void DoMember(const char* name, std::function<void(Reader&)> fn) override {
-    if (m_->GetType() != rapidjson::Type::kObjectType)
-      return;  // FIXME: signal an error that object was not deserialized
-               // correctly?
-
+    path_.push_back(name);
     auto it = m_->FindMember(name);
     if (it != m_->MemberEnd()) {
       JsonReader sub(&it->value);
       fn(sub);
     }
+    path_.pop_back();
+  }
+
+  std::string GetPath() const {
+    std::string ret;
+    for (auto& t : path_) {
+      ret += '/';
+      ret += t;
+    }
+    ret.pop_back();
+    return ret;
   }
 };
 
diff --git a/src/serializers/msgpack.h b/src/serializers/msgpack.h
index 91b08667..f9b1666b 100644
--- a/src/serializers/msgpack.h
+++ b/src/serializers/msgpack.h
@@ -21,6 +21,7 @@ class MessagePackReader : public Reader {
     return SerializeFormat::MessagePack;
   }
 
+  bool IsBool() override { return oh_.get().type == msgpack::type::BOOLEAN; }
   bool IsNull() override { return oh_.get().is_nil(); }
   bool IsArray() override { return oh_.get().type == msgpack::type::ARRAY; }
   bool IsInt() override {
@@ -28,6 +29,8 @@ class MessagePackReader : public Reader {
            oh_.get().type == msgpack::type::NEGATIVE_INTEGER;
   }
   bool IsInt64() override { return IsInt(); }
+  bool IsUint64() override { return IsInt(); }
+  bool IsDouble() override { return oh_.get().type == msgpack::type::FLOAT64; };
   bool IsString() override { return oh_.get().type == msgpack::type::STR; }
 
   void GetNull() override { pk_->next(oh_); }