diff --git a/dlib/array2d/array2d_kernel.h b/dlib/array2d/array2d_kernel.h
index 5a3f418b2..3e2b1468c 100644
--- a/dlib/array2d/array2d_kernel.h
+++ b/dlib/array2d/array2d_kernel.h
@@ -72,7 +72,7 @@ namespace dlib
                         - (*this)[x] == data[x]
             !*/
 
-            friend class array2d;
+            friend class array2d<T,mem_manager>;
             friend class row_helper;
 
         public:
diff --git a/dlib/dnn/cuda_dlib.cu b/dlib/dnn/cuda_dlib.cu
index c6e9a005e..ba78068e4 100644
--- a/dlib/dnn/cuda_dlib.cu
+++ b/dlib/dnn/cuda_dlib.cu
@@ -54,7 +54,7 @@ namespace dlib
         {
             int can_access;
             CHECK_CUDA(cudaDeviceCanAccessPeer(&can_access, device_id, peer_device_id));
-            return can_access;
+            return can_access != 0;
         }
         bool can_access_peer (const tensor& device, const tensor& peer_device)
         {
diff --git a/dlib/dnn/cuda_utils.h b/dlib/dnn/cuda_utils.h
index bc96c0f95..f34d188db 100644
--- a/dlib/dnn/cuda_utils.h
+++ b/dlib/dnn/cuda_utils.h
@@ -131,8 +131,8 @@ namespace dlib
 
         struct max_jobs
         {
-            max_jobs(size_t n) : num(n) {}
-            size_t num;
+            max_jobs(int n) : num(n) {}
+            int num;
         };
 
         template <typename Kernel, typename... T>
diff --git a/dlib/dnn/tensor.h b/dlib/dnn/tensor.h
index 46e2506e9..60959013c 100644
--- a/dlib/dnn/tensor.h
+++ b/dlib/dnn/tensor.h
@@ -137,7 +137,7 @@ namespace dlib
             const matrix_exp<EXP>& item
         )
         {
-            DLIB_CASSERT(idx < num_samples());
+            DLIB_CASSERT(idx < (unsigned long)num_samples());
             DLIB_CASSERT(item.size() == nr()*nc()*k());
             static_assert((is_same_type<float, typename EXP::type>::value == true),
                 "To assign a matrix to a tensor the matrix must contain float values");
diff --git a/dlib/matrix/matrix.h b/dlib/matrix/matrix.h
index 4b7b29801..542b11490 100644
--- a/dlib/matrix/matrix.h
+++ b/dlib/matrix/matrix.h
@@ -1751,7 +1751,7 @@ namespace dlib
 
             literal_assign_helper(const literal_assign_helper& item) : m(item.m), r(item.r), c(item.c), has_been_used(false) {}
             explicit literal_assign_helper(matrix* m_): m(m_), r(0), c(0),has_been_used(false) {next();}
-            ~literal_assign_helper() throw (std::exception)
+            ~literal_assign_helper() noexcept(false)
             {
                 DLIB_CASSERT(!has_been_used || r == m->nr(),
                              "You have used the matrix comma based assignment incorrectly by failing to\n"
@@ -1778,7 +1778,7 @@ namespace dlib
 
         private:
 
-            friend class matrix;
+            friend class matrix<T,num_rows,num_cols,mem_manager,layout>;
 
             void next (
             ) const