diff --git a/src/framework/operations.hpp b/src/framework/operations.hpp
index 17d8985fcb..f6c727c2b6 100644
--- a/src/framework/operations.hpp
+++ b/src/framework/operations.hpp
@@ -1775,7 +1775,7 @@ Op input_to_op_bfunc(const inputdata_t &input) {
   auto it = comp_table.find(relation);
   if (it == comp_table.end()) {
     std::stringstream msg;
-    msg << "Invalid bfunc relation string :\"" << it->first << "\"."
+    msg << "Invalid bfunc relation string :\"" << relation << "\"."
         << std::endl;
     throw std::invalid_argument(msg.str());
   } else {
diff --git a/src/simulators/density_matrix/densitymatrix_executor.hpp b/src/simulators/density_matrix/densitymatrix_executor.hpp
index 8a1081aa09..29c7fd52f1 100644
--- a/src/simulators/density_matrix/densitymatrix_executor.hpp
+++ b/src/simulators/density_matrix/densitymatrix_executor.hpp
@@ -1323,7 +1323,7 @@ Executor<densmat_t>::sample_measure(const reg_t &qubits, uint_t shots,
 #endif
 
   // Convert to SampleVector format
-  int_t npar = Base::parallel_state_update_;
+  uint_t npar = Base::parallel_state_update_;
   if (npar > local_samples.size())
     npar = local_samples.size();
   std::vector<SampleVector> all_samples(shots, SampleVector(qubits.size()));
diff --git a/src/simulators/density_matrix/densitymatrix_state.hpp b/src/simulators/density_matrix/densitymatrix_state.hpp
index 4300fed0db..ed0855b073 100644
--- a/src/simulators/density_matrix/densitymatrix_state.hpp
+++ b/src/simulators/density_matrix/densitymatrix_state.hpp
@@ -1003,7 +1003,7 @@ std::vector<SampleVector> State<densmat_t>::sample_measure(const reg_t &qubits,
   allbit_samples = BaseState::qreg_.sample_measure(rnds);
 
   // Convert to bit format
-  int_t npar = BaseState::threads_;
+  uint_t npar = BaseState::threads_;
   if (npar > shots)
     npar = shots;
   std::vector<SampleVector> all_samples(shots, SampleVector(qubits.size()));
diff --git a/src/simulators/state.hpp b/src/simulators/state.hpp
index 98b717222a..219eaa6bb0 100644
--- a/src/simulators/state.hpp
+++ b/src/simulators/state.hpp
@@ -259,7 +259,7 @@ class Base {
 
   // Maximum threads which may be used by the backend for OpenMP multithreading
   // Default value is single-threaded unless overridden
-  int threads_ = 1;
+  uint_t threads_ = 1;
 
   // Set a global phase exp(1j * theta) for the state
   bool has_global_phase_ = false;
diff --git a/src/simulators/statevector/statevector_executor.hpp b/src/simulators/statevector/statevector_executor.hpp
index 27193ff948..45777a0287 100644
--- a/src/simulators/statevector/statevector_executor.hpp
+++ b/src/simulators/statevector/statevector_executor.hpp
@@ -1241,7 +1241,7 @@ Executor<state_t>::sample_measure(const reg_t &qubits, uint_t shots,
 #endif
 
   // Convert to SampleVector format
-  int_t npar = Base::parallel_state_update_;
+  uint_t npar = Base::parallel_state_update_;
   if (npar > local_samples.size())
     npar = local_samples.size();
   std::vector<SampleVector> all_samples(shots, SampleVector(qubits.size()));