diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7deaeb5..f10fc3f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -617,7 +617,7 @@
 # GCC is not strict enough by default, so enable most of the warnings.
 IF ("${UNIX}")
   SET(CMAKE_CXX_FLAGS
-      "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wno-sign-compare -Wno-unused")
+      "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wno-unknown-pragmas -Wno-sign-compare -Wno-unused -Wno-unused-parameter")
 ENDIF ("${UNIX}")
 
 ADD_SUBDIRECTORY(internal/ceres)
diff --git a/internal/ceres/block_jacobi_preconditioner.h b/internal/ceres/block_jacobi_preconditioner.h
index 91cfedd..51f2655 100644
--- a/internal/ceres/block_jacobi_preconditioner.h
+++ b/internal/ceres/block_jacobi_preconditioner.h
@@ -37,7 +37,7 @@
 namespace ceres {
 namespace internal {
 
-class CompressedRowBlockStructure;
+struct CompressedRowBlockStructure;
 class LinearOperator;
 class SparseMatrix;
 
diff --git a/internal/ceres/canonical_views_clustering.h b/internal/ceres/canonical_views_clustering.h
index 2d1eb40..171ac55 100644
--- a/internal/ceres/canonical_views_clustering.h
+++ b/internal/ceres/canonical_views_clustering.h
@@ -52,7 +52,7 @@
 namespace ceres {
 namespace internal {
 
-class CanonicalViewsClusteringOptions;
+struct CanonicalViewsClusteringOptions;
 
 // Compute a partitioning of the vertices of the graph using the
 // canonical views clustering algorithm.
diff --git a/internal/ceres/compressed_row_sparse_matrix.h b/internal/ceres/compressed_row_sparse_matrix.h
index 6a9d828..10f96c0 100644
--- a/internal/ceres/compressed_row_sparse_matrix.h
+++ b/internal/ceres/compressed_row_sparse_matrix.h
@@ -42,7 +42,7 @@
 
 namespace ceres {
 
-class CRSMatrix;
+struct CRSMatrix;
 
 namespace internal {
 
diff --git a/internal/ceres/evaluator.h b/internal/ceres/evaluator.h
index 6aa30d7..3bbf50a 100644
--- a/internal/ceres/evaluator.h
+++ b/internal/ceres/evaluator.h
@@ -39,7 +39,7 @@
 
 namespace ceres {
 
-class CRSMatrix;
+struct CRSMatrix;
 
 namespace internal {
 
diff --git a/internal/ceres/triplet_sparse_matrix.cc b/internal/ceres/triplet_sparse_matrix.cc
index ed8677e..a09f38e 100644
--- a/internal/ceres/triplet_sparse_matrix.cc
+++ b/internal/ceres/triplet_sparse_matrix.cc
@@ -71,7 +71,8 @@
 }
 
 TripletSparseMatrix::TripletSparseMatrix(const TripletSparseMatrix& orig)
-    : num_rows_(orig.num_rows_),
+    : SparseMatrix(),
+      num_rows_(orig.num_rows_),
       num_cols_(orig.num_cols_),
       max_num_nonzeros_(orig.max_num_nonzeros_),
       num_nonzeros_(orig.num_nonzeros_),
diff --git a/internal/ceres/visibility.h b/internal/ceres/visibility.h
index 692dd87..f29e3c6 100644
--- a/internal/ceres/visibility.h
+++ b/internal/ceres/visibility.h
@@ -42,7 +42,7 @@
 namespace ceres {
 namespace internal {
 
-class CompressedRowBlockStructure;
+struct CompressedRowBlockStructure;
 
 // Given a compressed row block structure, computes the set of
 // e_blocks "visible" to each f_block. If an e_block co-occurs with an
diff --git a/internal/ceres/visibility_based_preconditioner.h b/internal/ceres/visibility_based_preconditioner.h
index 888c65e..3246fb8 100644
--- a/internal/ceres/visibility_based_preconditioner.h
+++ b/internal/ceres/visibility_based_preconditioner.h
@@ -69,7 +69,7 @@
 
 class BlockRandomAccessSparseMatrix;
 class BlockSparseMatrixBase;
-class CompressedRowBlockStructure;
+struct CompressedRowBlockStructure;
 class SchurEliminatorBase;
 
 // This class implements three preconditioners for Structure from