diff --git a/fec/fec.cpp b/fec/fec.cpp
index b194a173..102df038 100644
--- a/fec/fec.cpp
+++ b/fec/fec.cpp
@@ -19,6 +19,7 @@
 #include "fec.h"
 #include "td/utils/overloaded.h"
 #include "auto/tl/ton_api.hpp"
+#include "td/utils/misc.h"
 
 namespace ton {
 
@@ -98,24 +99,37 @@ td::uint32 FecType::symbol_size() const {
 }
 
 td::Result<FecType> FecType::create(tl_object_ptr<ton_api::fec_Type> obj) {
+  td::int32 data_size_int, symbol_size_int, symbols_count_int;
+  ton_api::downcast_call(*obj, td::overloaded([&](const auto &obj) {
+    data_size_int = obj.data_size_;
+    symbol_size_int = obj.symbol_size_;
+    symbols_count_int = obj.symbols_count_;
+  }));
+  TRY_RESULT(data_size, td::narrow_cast_safe<size_t>(data_size_int));
+  TRY_RESULT(symbol_size, td::narrow_cast_safe<size_t>(symbol_size_int));
+  TRY_RESULT(symbols_count, td::narrow_cast_safe<size_t>(symbols_count_int));
+
+  if (symbol_size == 0) {
+    return td::Status::Error("invalid fec type: symbol_size is 0");
+  }
+  if (symbol_size > 1 << 11) {
+    return td::Status::Error("invalid fec type: symbol_size is too big");
+  }
+  if (symbols_count != (data_size + symbol_size - 1) / symbol_size) {
+    return td::Status::Error("invalid fec type: wrong symbols_count");
+  }
   FecType T;
-  ton_api::downcast_call(
-      *obj.get(), td::overloaded(
-                      [&](const ton_api::fec_raptorQ &obj) {
-                        T.type_ = td::fec::RaptorQEncoder::Parameters{static_cast<size_t>(obj.data_size_),
-                                                                      static_cast<size_t>(obj.symbol_size_),
-                                                                      static_cast<size_t>(obj.symbols_count_)};
-                      },
-                      [&](const ton_api::fec_roundRobin &obj) {
-                        T.type_ = td::fec::RoundRobinEncoder::Parameters{static_cast<size_t>(obj.data_size_),
-                                                                         static_cast<size_t>(obj.symbol_size_),
-                                                                         static_cast<size_t>(obj.symbols_count_)};
-                      },
-                      [&](const ton_api::fec_online &obj) {
-                        T.type_ = td::fec::OnlineEncoder::Parameters{static_cast<size_t>(obj.data_size_),
-                                                                     static_cast<size_t>(obj.symbol_size_),
-                                                                     static_cast<size_t>(obj.symbols_count_)};
-                      }));
+  ton_api::downcast_call(*obj,
+                         td::overloaded(
+                             [&](const ton_api::fec_raptorQ &obj) {
+                               T.type_ = td::fec::RaptorQEncoder::Parameters{data_size, symbol_size, symbols_count};
+                             },
+                             [&](const ton_api::fec_roundRobin &obj) {
+                               T.type_ = td::fec::RoundRobinEncoder::Parameters{data_size, symbol_size, symbols_count};
+                             },
+                             [&](const ton_api::fec_online &obj) {
+                               T.type_ = td::fec::OnlineEncoder::Parameters{data_size, symbol_size, symbols_count};
+                             }));
   return T;
 }
 
diff --git a/overlay/overlay-fec-broadcast.cpp b/overlay/overlay-fec-broadcast.cpp
index 7ff08309..aed5248b 100644
--- a/overlay/overlay-fec-broadcast.cpp
+++ b/overlay/overlay-fec-broadcast.cpp
@@ -28,8 +28,8 @@ td::Result<std::unique_ptr<BroadcastFec>> BroadcastFec::create(Overlay::Broadcas
                                                                Overlay::BroadcastDataHash data_hash, td::uint32 flags,
                                                                td::uint32 date, fec::FecType fec_type) {
   auto F = std::make_unique<BroadcastFec>(hash, std::move(src), data_hash, flags, date, std::move(fec_type));
-  TRY_STATUS(F->init_fec_type());
   TRY_STATUS(F->run_checks());
+  TRY_STATUS(F->init_fec_type());
   return std::move(F);
 }
 
diff --git a/rldp/rldp-peer.cpp b/rldp/rldp-peer.cpp
index 6192d070..c599e949 100644
--- a/rldp/rldp-peer.cpp
+++ b/rldp/rldp-peer.cpp
@@ -125,6 +125,10 @@ void RldpTransferReceiverImpl::receive_part(fec::FecType fec_type, td::uint32 pa
   }
 
   if (!decoder_) {
+    if (offset_ + fec_type.size() > total_size_) {
+      VLOG(RLDP_NOTICE) << "failed to create decoder: data size in fec type is too big";
+      return;
+    }
     auto D = fec_type.create_decoder();
     if (D.is_error()) {
       VLOG(RLDP_WARNING) << "failed to create decoder: " << D.move_as_error();