diff --git a/cogl/cogl-matrix.h b/cogl/cogl-matrix.h
index 80b828e66..0d6d72752 100644
--- a/cogl/cogl-matrix.h
+++ b/cogl/cogl-matrix.h
@@ -28,6 +28,7 @@
 #define __COGL_MATRIX_H
 
 #include <glib.h>
+#include "cogl-types.h"
 
 G_BEGIN_DECLS
 
@@ -100,10 +101,10 @@ struct _CoglMatrix
 
   /* Note: we may want to extend this later with private flags
    * and a cache of the inverse transform matrix. */
-  float   inv[16];
-  unsigned long  type;
-  unsigned long  flags;
-  unsigned long  _padding3;
+  float          COGL_PRIVATE (inv)[16];
+  unsigned long  COGL_PRIVATE (type);
+  unsigned long  COGL_PRIVATE (flags);
+  unsigned long  COGL_PRIVATE (_padding3);
 };
 
 /**
diff --git a/cogl/cogl-types.h b/cogl/cogl-types.h
index b45bad41e..547ed129a 100644
--- a/cogl/cogl-types.h
+++ b/cogl/cogl-types.h
@@ -32,6 +32,16 @@
 
 G_BEGIN_DECLS
 
+/* Some structures are meant to be opaque but they have public
+   definitions because we want the size to be public so they can be
+   allocated on the stack. This macro is used to ensure that users
+   don't accidentally access private members */
+#ifdef CLUTTER_COMPILATION
+#define COGL_PRIVATE(x) x
+#else
+#define COGL_PRIVATE(x) private_member_ ## x
+#endif
+
 /**
  * CoglHandle:
  *
@@ -251,17 +261,17 @@ typedef enum
 struct _CoglColor
 {
   /*< private >*/
-  guint8 red;
-  guint8 green;
-  guint8 blue;
+  guint8 COGL_PRIVATE (red);
+  guint8 COGL_PRIVATE (green);
+  guint8 COGL_PRIVATE (blue);
 
-  guint8 alpha;
+  guint8 COGL_PRIVATE (alpha);
 
   /* padding in case we want to change to floats at
    * some point */
-  guint32 padding0;
-  guint32 padding1;
-  guint32 padding2;
+  guint32 COGL_PRIVATE (padding0);
+  guint32 COGL_PRIVATE (padding1);
+  guint32 COGL_PRIVATE (padding2);
 };
 
 /**