diff --git a/openvdb/viewer/ClipBox.h b/openvdb/viewer/ClipBox.h
index ad62d39..c68c5be 100644
--- a/openvdb/viewer/ClipBox.h
+++ b/openvdb/viewer/ClipBox.h
@@ -37,6 +37,7 @@
 #include <OpenGL/gl.h>
 #include <OpenGL/glu.h>
 #else
+#include <windows.h>
 #include <GL/gl.h>
 #include <GL/glu.h>
 #endif
diff --git a/openvdb/viewer/Font.h b/openvdb/viewer/Font.h
index da62993..b341165 100644
--- a/openvdb/viewer/Font.h
+++ b/openvdb/viewer/Font.h
@@ -37,6 +37,7 @@
 #include <OpenGL/gl.h>
 #include <OpenGL/glu.h>
 #else
+#include <windows.h>
 #include <GL/gl.h>
 #include <GL/glu.h>
 #endif
diff --git a/openvdb/viewer/RenderModules.h b/openvdb/viewer/RenderModules.h
index b9fa5b1..fd38a50 100644
--- a/openvdb/viewer/RenderModules.h
+++ b/openvdb/viewer/RenderModules.h
@@ -31,6 +31,7 @@
 #ifndef OPENVDB_VIEWER_RENDERMODULES_HAS_BEEN_INCLUDED
 #define OPENVDB_VIEWER_RENDERMODULES_HAS_BEEN_INCLUDED
 
+#include <GL/glew.h>
 #include <openvdb/openvdb.h>
 #include <openvdb/tools/VolumeToMesh.h>
 #include <openvdb/tools/MeshToVolume.h>
@@ -41,6 +42,7 @@
 #include <vector>
 
 #if defined(__APPLE__) || defined(MACOSX)
+#include <windows.h>
 #include <OpenGL/gl.h>
 #include <OpenGL/glu.h>
 #else
diff --git a/openvdb/viewer/Viewer.cc b/openvdb/viewer/Viewer.cc
index 31bb7a4..88bd308 100644
--- a/openvdb/viewer/Viewer.cc
+++ b/openvdb/viewer/Viewer.cc
@@ -31,9 +31,9 @@
 #include "Viewer.h"
 
 #include "Camera.h"
+#include "RenderModules.h"
 #include "ClipBox.h"
 #include "Font.h"
-#include "RenderModules.h"
 #include <openvdb/util/Formats.h> // for formattedInt()
 #include <openvdb/util/logging.h>
 #include <openvdb/points/PointDataGrid.h>