diff --git a/internal/ceres/block_jacobian_writer.cc b/internal/ceres/block_jacobian_writer.cc
index 2b1742a..727d649 100644
--- a/internal/ceres/block_jacobian_writer.cc
+++ b/internal/ceres/block_jacobian_writer.cc
@@ -138,12 +138,12 @@
 // Create evaluate prepareres that point directly into the final jacobian. This
 // makes the final Write() a nop.
 std::unique_ptr<BlockEvaluatePreparer[]>
-BlockJacobianWriter::CreateEvaluatePreparers(int num_threads) {
+BlockJacobianWriter::CreateEvaluatePreparers(unsigned num_threads) {
   int max_derivatives_per_residual_block =
       program_->MaxDerivativesPerResidualBlock();
 
   auto preparers = std::make_unique<BlockEvaluatePreparer[]>(num_threads);
-  for (int i = 0; i < num_threads; i++) {
+  for (unsigned i = 0; i < num_threads; i++) {
     preparers[i].Init(&jacobian_layout_[0], max_derivatives_per_residual_block);
   }
   return preparers;
diff --git a/internal/ceres/block_jacobian_writer.h b/internal/ceres/block_jacobian_writer.h
index 00dcb36..7f5c50b 100644
--- a/internal/ceres/block_jacobian_writer.h
+++ b/internal/ceres/block_jacobian_writer.h
@@ -60,7 +60,7 @@
   // Create evaluate prepareres that point directly into the final jacobian.
   // This makes the final Write() a nop.
   std::unique_ptr<BlockEvaluatePreparer[]> CreateEvaluatePreparers(
-      int num_threads);
+      unsigned num_threads);
 
   std::unique_ptr<SparseMatrix> CreateJacobian() const;
 
diff --git a/internal/ceres/program_evaluator.h b/internal/ceres/program_evaluator.h
index 826a73a..1176bb8 100644
--- a/internal/ceres/program_evaluator.h
+++ b/internal/ceres/program_evaluator.h
@@ -1,5 +1,5 @@
 // Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2015 Google Inc. All rights reserved.
+// Copyright 2022 Google Inc. All rights reserved.
 // http://ceres-solver.org/
 //
 // Redistribution and use in source and binary forms, with or without
@@ -129,8 +129,8 @@
 #endif  // CERES_NO_THREADS
 
     BuildResidualLayout(*program, &residual_layout_);
-    evaluate_scratch_ =
-        std::move(CreateEvaluatorScratch(*program, options.num_threads));
+    evaluate_scratch_ = std::move(CreateEvaluatorScratch(
+        *program, static_cast<unsigned>(options.num_threads)));
   }
 
   // Implementation of Evaluator interface.
@@ -345,7 +345,7 @@
 
   // Create scratch space for each thread evaluating the program.
   static std::unique_ptr<EvaluateScratch[]> CreateEvaluatorScratch(
-      const Program& program, int num_threads) {
+      const Program& program, unsigned num_threads) {
     int max_parameters_per_residual_block =
         program.MaxParametersPerResidualBlock();
     int max_scratch_doubles_needed_for_evaluate =
diff --git a/internal/ceres/scratch_evaluate_preparer.cc b/internal/ceres/scratch_evaluate_preparer.cc
index 680dab9..f20f8fc 100644
--- a/internal/ceres/scratch_evaluate_preparer.cc
+++ b/internal/ceres/scratch_evaluate_preparer.cc
@@ -1,5 +1,5 @@
 // Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2015 Google Inc. All rights reserved.
+// Copyright 2022 Google Inc. All rights reserved.
 // http://ceres-solver.org/
 //
 // Redistribution and use in source and binary forms, with or without
@@ -39,19 +39,19 @@
 namespace ceres::internal {
 
 std::unique_ptr<ScratchEvaluatePreparer[]> ScratchEvaluatePreparer::Create(
-    const Program& program, int num_threads) {
+    const Program& program, unsigned num_threads) {
   auto preparers = std::make_unique<ScratchEvaluatePreparer[]>(num_threads);
   int max_derivatives_per_residual_block =
       program.MaxDerivativesPerResidualBlock();
-  for (int i = 0; i < num_threads; i++) {
+  for (unsigned i = 0; i < num_threads; i++) {
     preparers[i].Init(max_derivatives_per_residual_block);
   }
   return preparers;
 }
 
 void ScratchEvaluatePreparer::Init(int max_derivatives_per_residual_block) {
-  jacobian_scratch_ =
-      std::make_unique<double[]>(max_derivatives_per_residual_block);
+  jacobian_scratch_ = std::make_unique<double[]>(
+      static_cast<std::size_t>(max_derivatives_per_residual_block));
 }
 
 // Point the jacobian blocks into the scratch area of this evaluate preparer.
diff --git a/internal/ceres/scratch_evaluate_preparer.h b/internal/ceres/scratch_evaluate_preparer.h
index 946244b..dbd4e50 100644
--- a/internal/ceres/scratch_evaluate_preparer.h
+++ b/internal/ceres/scratch_evaluate_preparer.h
@@ -1,5 +1,5 @@
 // Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2015 Google Inc. All rights reserved.
+// Copyright 2022 Google Inc. All rights reserved.
 // http://ceres-solver.org/
 //
 // Redistribution and use in source and binary forms, with or without
@@ -50,7 +50,7 @@
  public:
   // Create num_threads ScratchEvaluatePreparers.
   static std::unique_ptr<ScratchEvaluatePreparer[]> Create(
-      const Program& program, int num_threads);
+      const Program& program, unsigned num_threads);
 
   // EvaluatePreparer interface
   void Init(int max_derivatives_per_residual_block);