diff --git a/.travis.yml b/.travis.yml
index 438bf4d0..503d678a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -77,8 +77,7 @@ script:
   - if [[ "$TRAVIS_OS_NAME" != "linux" || "$COMP" == "gcc" ]]; then make clean && make -j2 ARCH=x86-64-modern profile-build && ../tests/signature.sh $benchref; fi
 
   # start some basic learner CI
-  #TODO enable -Werror
-  - export CXXFLAGS=""
+  - export CXXFLAGS="-Werror"
   - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then make clean && LDFLAGS="-lstdc++fs" make -j2 ARCH=x86-64-modern learn; fi
   - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then make clean && LDFLAGS="-lstdc++fs" make -j2 ARCH=x86-64-modern profile-learn; fi
 
diff --git a/src/learn/gensfen.cpp b/src/learn/gensfen.cpp
index 3d015acf..84feabb0 100644
--- a/src/learn/gensfen.cpp
+++ b/src/learn/gensfen.cpp
@@ -878,8 +878,7 @@ namespace Learner
                     next_move = search_pv[0];
                 }
 
-            RANDOM_MOVE:;
-
+                // Random move.
                 auto random_move = choose_random_move(pos, random_move_flag, ply, actual_random_move_count);
                 if (random_move.has_value())
                 {
@@ -897,7 +896,7 @@ namespace Learner
                     a_psv.clear();
                 }
 
-            DO_MOVE:;
+                // Do move.
                 pos.do_move(next_move, states[ply]);
 
                 // Call node evaluate() for each difference calculation.
diff --git a/src/nnue/evaluate_nnue_learner.cpp b/src/nnue/evaluate_nnue_learner.cpp
index 7be06832..8b0413e5 100644
--- a/src/nnue/evaluate_nnue_learner.cpp
+++ b/src/nnue/evaluate_nnue_learner.cpp
@@ -113,8 +113,13 @@ void SetOptions(const std::string& options) {
 void RestoreParameters(const std::string& dir_name) {
   const std::string file_name = Path::Combine(dir_name, NNUE::savedfileName);
   std::ifstream stream(file_name, std::ios::binary);
-  bool result = ReadParameters(stream);
+#ifndef NDEBUG
+  bool result =
+#endif
+  ReadParameters(stream);
+#ifndef NDEBUG
   assert(result);
+#endif
 
   SendMessages({{"reset"}});
 }
@@ -216,8 +221,13 @@ void save_eval(std::string dir_name) {
 
   const std::string file_name = Path::Combine(eval_dir, NNUE::savedfileName);
   std::ofstream stream(file_name, std::ios::binary);
-  const bool result = NNUE::WriteParameters(stream);
+#ifndef NDEBUG
+  const bool result =
+#endif
+  NNUE::WriteParameters(stream);
+#ifndef NDEBUG
   assert(result);
+#endif
 
   std::cout << "save_eval() finished. folder = " << eval_dir << std::endl;
 }
diff --git a/src/nnue/trainer/trainer.h b/src/nnue/trainer/trainer.h
index d526557a..94553c07 100644
--- a/src/nnue/trainer/trainer.h
+++ b/src/nnue/trainer/trainer.h
@@ -70,8 +70,8 @@ struct Example {
 
 // Message used for setting hyperparameters
 struct Message {
-  Message(const std::string& name, const std::string& value = ""):
-      name(name), value(value), num_peekers(0), num_receivers(0) {}
+  Message(const std::string& message_name, const std::string& message_value = ""):
+      name(message_name), value(message_value), num_peekers(0), num_receivers(0) {}
   const std::string name;
   const std::string value;
   std::uint32_t num_peekers;
diff --git a/src/nnue/trainer/trainer_input_slice.h b/src/nnue/trainer/trainer_input_slice.h
index b6d6635b..6b0adc9f 100644
--- a/src/nnue/trainer/trainer_input_slice.h
+++ b/src/nnue/trainer/trainer_input_slice.h
@@ -206,7 +206,7 @@ class Trainer<Layers::InputSlice<OutputDimensions, Offset>> {
       const IndexType input_offset = kInputDimensions * b;
       const IndexType output_offset = kOutputDimensions * b;
       for (IndexType i = 0; i < kInputDimensions; ++i) {
-        if (i < Offset || i >= Offset + kOutputDimensions) {
+        if ((int)i < (int)Offset || i >= Offset + kOutputDimensions) {
           gradients_[input_offset + i] = static_cast<LearnFloatType>(0.0);
         } else {
           gradients_[input_offset + i] = gradients[output_offset + i - Offset];