diff --git a/dlls/kernel/atom.c b/dlls/kernel/atom.c
index 2915b3f5aa5..32f86de21d5 100644
--- a/dlls/kernel/atom.c
+++ b/dlls/kernel/atom.c
@@ -42,7 +42,7 @@
 #include "wine/unicode.h"
 #include "wine/winbase16.h"
 #include "global.h"
-#include "instance.h"
+#include "kernel_private.h"
 #include "stackframe.h"
 
 #include "wine/debug.h"
diff --git a/dlls/kernel/device.c b/dlls/kernel/device.c
index 1056529bd4f..58d0b561566 100644
--- a/dlls/kernel/device.c
+++ b/dlls/kernel/device.c
@@ -43,9 +43,9 @@
 #include "winnt.h"
 #include "msdos.h"
 #include "miscemu.h"
+#include "kernel_private.h"
 #include "wine/server.h"
 #include "wine/debug.h"
-#include "callback.h"
 
 WINE_DEFAULT_DEBUG_CHANNEL(file);
 
diff --git a/dlls/kernel/instr.c b/dlls/kernel/instr.c
index 80496771aeb..6bfcad53b1f 100644
--- a/dlls/kernel/instr.c
+++ b/dlls/kernel/instr.c
@@ -30,7 +30,7 @@
 #include "miscemu.h"
 #include "selectors.h"
 #include "wine/debug.h"
-#include "callback.h"
+#include "kernel_private.h"
 #include "thread.h"
 #include "wine/exception.h"
 
diff --git a/dlls/kernel/kernel_private.h b/dlls/kernel/kernel_private.h
index 71f3db34438..a38c384cd1b 100644
--- a/dlls/kernel/kernel_private.h
+++ b/dlls/kernel/kernel_private.h
@@ -53,4 +53,30 @@ extern BOOL WOWTHUNK_Init(void);
 
 extern VOID SYSLEVEL_CheckNotLevel( INT level );
 
+typedef struct
+{
+    void (WINAPI *EmulateInterruptPM)( CONTEXT86 *context, BYTE intnum );
+    void (WINAPI *CallBuiltinHandler)( CONTEXT86 *context, BYTE intnum );
+
+    /* I/O functions */
+    DWORD (WINAPI *inport)( int port, int size );
+    void (WINAPI *outport)( int port, int size, DWORD val );
+} DOSVM_TABLE;
+
+extern DOSVM_TABLE Dosvm;
+
+/* this structure is always located at offset 0 of the DGROUP segment */
+#include "pshpack1.h"
+typedef struct
+{
+    WORD null;        /* Always 0 */
+    DWORD old_ss_sp;  /* Stack pointer; used by SwitchTaskTo() */
+    WORD heap;        /* Pointer to the local heap information (if any) */
+    WORD atomtable;   /* Pointer to the local atom table (if any) */
+    WORD stacktop;    /* Top of the stack */
+    WORD stackmin;    /* Lowest stack address used so far */
+    WORD stackbottom; /* Bottom of the stack */
+} INSTANCEDATA;
+#include "poppack.h"
+
 #endif
diff --git a/dlls/kernel/local16.c b/dlls/kernel/local16.c
index 7baf01fc316..5015b31a56f 100644
--- a/dlls/kernel/local16.c
+++ b/dlls/kernel/local16.c
@@ -35,13 +35,13 @@
 #include <string.h>
 #include "wine/winbase16.h"
 #include "wownt32.h"
-#include "instance.h"
 #include "local.h"
 #include "global.h"
 #include "module.h"
 #include "stackframe.h"
 #include "selectors.h"
 #include "toolhelp.h"
+#include "kernel_private.h"
 #include "wine/debug.h"
 
 WINE_DEFAULT_DEBUG_CHANNEL(local);
diff --git a/dlls/kernel/task.c b/dlls/kernel/task.c
index ad9fa2b7016..74f8f7f8727 100644
--- a/dlls/kernel/task.c
+++ b/dlls/kernel/task.c
@@ -40,7 +40,6 @@
 #include "drive.h"
 #include "file.h"
 #include "global.h"
-#include "instance.h"
 #include "module.h"
 #include "winternl.h"
 #include "selectors.h"
diff --git a/dlls/kernel/vxd.c b/dlls/kernel/vxd.c
index dc2db836640..bb86ab605a7 100644
--- a/dlls/kernel/vxd.c
+++ b/dlls/kernel/vxd.c
@@ -40,7 +40,7 @@
 #include "winnt.h"
 #include "winternl.h"
 #include "miscemu.h"
-#include "callback.h"
+#include "kernel_private.h"
 #include "wine/debug.h"
 
 WINE_DEFAULT_DEBUG_CHANNEL(vxd);
diff --git a/include/callback.h b/include/callback.h
deleted file mode 100644
index 018c6e32af2..00000000000
--- a/include/callback.h
+++ /dev/null
@@ -1,40 +0,0 @@
-/*
- * Callback functions
- *
- * Copyright 1995 Alexandre Julliard
- *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation; either
- * version 2.1 of the License, or (at your option) any later version.
- *
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
- */
-
-#ifndef __WINE_CALLBACK_H
-#define __WINE_CALLBACK_H
-
-#include <stdarg.h>
-#include <windef.h>
-#include <winbase.h>
-#include <winnt.h>
-
-typedef struct {
-    void (WINAPI *EmulateInterruptPM)( CONTEXT86 *context, BYTE intnum );
-    void (WINAPI *CallBuiltinHandler)( CONTEXT86 *context, BYTE intnum );
-
-    /* I/O functions */
-    DWORD (WINAPI *inport)( int port, int size );
-    void (WINAPI *outport)( int port, int size, DWORD val );
-} DOSVM_TABLE;
-
-extern DOSVM_TABLE Dosvm;
-
-#endif /* __WINE_CALLBACK_H */
diff --git a/include/instance.h b/include/instance.h
deleted file mode 100644
index 78f35c34a28..00000000000
--- a/include/instance.h
+++ /dev/null
@@ -1,39 +0,0 @@
-/*
- * Instance data declaration
- *
- * Copyright 1995 Alexandre Julliard
- *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation; either
- * version 2.1 of the License, or (at your option) any later version.
- *
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
- */
-
-#ifndef __WINE_INSTANCE_H
-#define __WINE_INSTANCE_H
-
-#include <windef.h>
-
-  /* This structure is always located at offset 0 of the DGROUP segment */
-
-typedef struct
-{
-    WORD null;        /* Always 0 */
-    DWORD old_ss_sp WINE_PACKED;  /* Stack pointer; used by SwitchTaskTo() */
-    WORD heap;        /* Pointer to the local heap information (if any) */
-    WORD atomtable;   /* Pointer to the local atom table (if any) */
-    WORD stacktop;    /* Top of the stack */
-    WORD stackmin;    /* Lowest stack address used so far */
-    WORD stackbottom; /* Bottom of the stack */
-} INSTANCEDATA;
-
-#endif /* __WINE_INSTANCE_H */
diff --git a/msdos/dpmi.c b/msdos/dpmi.c
index 7ae2177d550..d1693a95f24 100644
--- a/msdos/dpmi.c
+++ b/msdos/dpmi.c
@@ -25,7 +25,7 @@
 
 #include "windef.h"
 #include "winbase.h"
-#include "callback.h"
+#include "kernel_private.h"
 #include "wine/debug.h"
 #include "wine/windef16.h"
 
diff --git a/msdos/int21.c b/msdos/int21.c
index 4115a5f95b0..0ab3a926587 100644
--- a/msdos/int21.c
+++ b/msdos/int21.c
@@ -55,10 +55,10 @@
 #include "winerror.h"
 #include "drive.h"
 #include "file.h"
-#include "callback.h"
 #include "msdos.h"
 #include "miscemu.h"
 #include "task.h"
+#include "kernel_private.h"
 #include "wine/unicode.h"
 #include "wine/debug.h"