diff --git a/include/bout/field.hxx b/include/bout/field.hxx
index 863163ce60..d56322070e 100644
--- a/include/bout/field.hxx
+++ b/include/bout/field.hxx
@@ -31,6 +31,7 @@ class Field;
 
 #include <cmath>
 #include <cstdio>
+#include <optional>
 #include <string>
 
 #include "bout/bout_types.hxx"
diff --git a/src/solver/impls/euler/euler.cxx b/src/solver/impls/euler/euler.cxx
index 5477b5760b..709ac5ba9b 100644
--- a/src/solver/impls/euler/euler.cxx
+++ b/src/solver/impls/euler/euler.cxx
@@ -6,6 +6,7 @@
 #include <bout/msg_stack.hxx>
 #include <bout/openmpwrap.hxx>
 #include <bout/utils.hxx>
+#include <bout/version.hxx>
 
 #include <cmath>
 
diff --git a/src/solver/impls/pvode/pvode.cxx b/src/solver/impls/pvode/pvode.cxx
index 7524d21238..65d44d6e49 100644
--- a/src/solver/impls/pvode/pvode.cxx
+++ b/src/solver/impls/pvode/pvode.cxx
@@ -35,6 +35,7 @@
 #include <bout/msg_stack.hxx>
 #include <bout/output.hxx>
 #include <bout/sys/timer.hxx>
+#include <bout/version.hxx>
 
 #include "bout/unused.hxx"