diff --git a/cpp/demo/poisson/main.cpp b/cpp/demo/poisson/main.cpp
index 1ae9307f3ce..64644229b61 100644
--- a/cpp/demo/poisson/main.cpp
+++ b/cpp/demo/poisson/main.cpp
@@ -85,6 +85,8 @@
 #include <dolfinx.h>
 #include <dolfinx/fem/Constant.h>
 #include <dolfinx/fem/petsc.h>
+#include <dolfinx/la/petsc.h>
+#include <petscmat.h>
 #include <petscsys.h>
 #include <petscsystypes.h>
 #include <utility>