diff --git a/Source/exehead/Ui.c b/Source/exehead/Ui.c
index 7bc1e458..4590bea9 100644
--- a/Source/exehead/Ui.c
+++ b/Source/exehead/Ui.c
@@ -302,7 +302,7 @@ FORCE_INLINE int NSISCALL ui_doinstall(void)
 
 #ifdef NSIS_SUPPORT_CODECALLBACKS
   // Select language
-  if (ExecuteCodeSegment(header->code_onInit,NULL)) return 1;
+  if (ExecuteCallbackFunction(CB_ONINIT)) return 1;
   set_language();
 #endif
 
@@ -347,7 +347,7 @@ FORCE_INLINE int NSISCALL ui_doinstall(void)
     {
       int ret=DialogBox(g_hInstance,MAKEINTRESOURCE(IDD_INST+dlg_offset),0,DialogProc);
 #if defined(NSIS_SUPPORT_CODECALLBACKS) && defined(NSIS_CONFIG_ENHANCEDUI_SUPPORT)
-      ExecuteCodeSegment(header->code_onGUIEnd,NULL);
+      ExecuteCallbackFunction(CB_ONGUIEND);
 #endif
       return ret;
     }
@@ -361,12 +361,12 @@ FORCE_INLINE int NSISCALL ui_doinstall(void)
     if (install_thread(NULL))
     {
 #ifdef NSIS_SUPPORT_CODECALLBACKS
-      if (!g_quit_flag) ExecuteCodeSegment(header->code_onInstFailed,NULL);
+      if (!g_quit_flag) ExecuteCallbackFunction(CB_ONINSTFAILED);
 #endif//NSIS_SUPPORT_CODECALLBACKS
       return 1;
     }
 #ifdef NSIS_SUPPORT_CODECALLBACKS
-    ExecuteCodeSegment(header->code_onInstSuccess,NULL);
+    ExecuteCallbackFunction(CB_ONINSTSUCCESS);
 #endif//NSIS_SUPPORT_CODECALLBACKS
 
     return 0;
@@ -391,7 +391,7 @@ static int CALLBACK WINAPI BrowseCallbackProc(HWND hwnd, UINT uMsg, LPARAM lPara
       0,
       SHGetPathFromIDList((LPITEMIDLIST)lParam,(char*)lpData)
 #ifdef NSIS_SUPPORT_CODECALLBACKS
-      && !ExecuteCodeSegment(g_header->code_onVerifyInstDir,NULL)
+      && !ExecuteCallbackFunction(CB_ONVERIFYINSTDIR)
 #endif
     );
   }
@@ -428,7 +428,7 @@ BOOL CALLBACK DialogProc(HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lParam)
       SetDlgItemTextFromLang(hwndDlg,IDC_VERSTR,LANG_BRANDING);
       SetClassLong(hwndDlg,GCL_HICON,(long)g_hIcon);
 #if defined(NSIS_SUPPORT_CODECALLBACKS) && defined(NSIS_CONFIG_ENHANCEDUI_SUPPORT)
-      g_quit_flag = ExecuteCodeSegment(g_header->code_onGUIInit,NULL);
+      g_quit_flag = ExecuteCallbackFunction(CB_ONGUIINIT);
 #endif
         //ShowWindow(hwndDlg, SW_SHOW);
       m_delta = 1;
@@ -456,7 +456,7 @@ nextPage:
     this_page+=m_delta;
 
 #ifdef NSIS_SUPPORT_CODECALLBACKS
-    if (m_page==g_blocks[NB_PAGES].num) ExecuteCodeSegment(g_header->code_onInstSuccess,NULL);
+    if (m_page==g_blocks[NB_PAGES].num) ExecuteCallbackFunction(CB_ONINSTSUCCESS);
 #endif//NSIS_SUPPORT_CODECALLBACKS
 
     if (g_quit_flag || (unsigned int)m_page >= (unsigned int)g_blocks[NB_PAGES].num)
@@ -609,7 +609,7 @@ skipPage:
       if (g_exec_flags.abort)
       {
 #ifdef NSIS_SUPPORT_CODECALLBACKS
-        ExecuteCodeSegment(g_header->code_onInstFailed,NULL);
+        ExecuteCallbackFunction(CB_ONINSTFAILED);
 #endif//NSIS_SUPPORT_CODECALLBACKS
         m_retcode=2;
         outernotify(NOTIFY_BYE_BYE);
@@ -617,7 +617,7 @@ skipPage:
       else
       {
 #ifdef NSIS_SUPPORT_CODECALLBACKS
-        if (!ExecuteCodeSegment(g_header->code_onUserAbort,NULL))
+        if (!ExecuteCallbackFunction(CB_ONUSERABORT))
 #endif//NSIS_SUPPORT_CODECALLBACKS
         {
           m_retcode=1;
@@ -935,7 +935,7 @@ static BOOL CALLBACK DirProc(HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPar
 
 #ifdef NSIS_SUPPORT_CODECALLBACKS
     if (!error)
-      error = ExecuteCodeSegment(g_header->code_onVerifyInstDir,NULL);
+      error = ExecuteCallbackFunction(CB_ONVERIFYINSTDIR);
 #endif
 
     if (thispage->flags & PF_DIR_NO_BTN_DISABLE)
@@ -1101,7 +1101,7 @@ static DWORD WINAPI newTreeWndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM l
 
       myitoa(g_usrvars[0], lParam);
 
-      ExecuteCodeSegment(g_header->code_onMouseOverSection,NULL);
+      ExecuteCallbackFunction(CB_ONMOUSEOVERSECTION);
 
       mystrcpy(g_usrvars[0], g_tmp);
     }
@@ -1400,7 +1400,7 @@ static BOOL CALLBACK SelProc(HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPar
   {
 #if defined(NSIS_SUPPORT_CODECALLBACKS) && defined(NSIS_CONFIG_COMPONENTPAGE)
   if ( wParam )
-    ExecuteCodeSegment(g_header->code_onSelChange,NULL);
+    ExecuteCallbackFunction(CB_ONSELCHANGE);
 #endif//NSIS_SUPPORT_CODECALLBACKS && NSIS_CONFIG_COMPONENTPAGE
 
     if (g_flags & CH_FLAGS_COMP_ONLY_ON_CUSTOM)
diff --git a/Source/exehead/exec.c b/Source/exehead/exec.c
index 55bf8c76..4920fbbd 100644
--- a/Source/exehead/exec.c
+++ b/Source/exehead/exec.c
@@ -64,6 +64,11 @@ int NSISCALL ExecuteCodeSegment(int pos, HWND hwndProgress)
   return 0;
 }
 
+int NSISCALL ExecuteCallbackFunction(int num)
+{
+  return ExecuteCodeSegment(*(&g_header->code_onInit + num), NULL);
+}
+
 static char bufs[5][NSIS_MAX_STRLEN];
 static int *parms;
 
diff --git a/Source/exehead/exec.h b/Source/exehead/exec.h
index ce7c7032..9c18c9e3 100644
--- a/Source/exehead/exec.h
+++ b/Source/exehead/exec.h
@@ -4,5 +4,6 @@
 extern exec_flags g_exec_flags;
 
 int NSISCALL ExecuteCodeSegment(int pos, HWND hwndProgress); // returns 0 on success
+int NSISCALL ExecuteCallbackFunction(int num); // returns 0 on success
 
 #endif//_EXEC_H_
diff --git a/Source/exehead/fileform.h b/Source/exehead/fileform.h
index 5ba28fed..fef87017 100644
--- a/Source/exehead/fileform.h
+++ b/Source/exehead/fileform.h
@@ -309,6 +309,28 @@ typedef struct
   int install_directory_auto_append; // auto append part
 } header;
 
+#ifdef NSIS_SUPPORT_CODECALLBACKS
+// callback indices
+enum
+{
+  CB_ONINIT,
+  CB_ONINSTSUCCESS,
+  CB_ONINSTFAILED,
+  CB_ONUSERABORT,
+#ifdef NSIS_CONFIG_ENHANCEDUI_SUPPORT
+  CB_ONGUIINIT,
+  CB_ONGUIEND,
+#endif
+  CB_ONVERIFYINSTDIR,
+#ifdef NSIS_CONFIG_ENHANCEDUI_SUPPORT
+  CB_ONMOUSEOVERSECTION,
+#endif
+#ifdef NSIS_CONFIG_COMPONENTPAGE
+  CB_ONSELCHANGE
+#endif//NSIS_CONFIG_COMPONENTPAGE
+};
+#endif//NSIS_SUPPORT_CODECALLBACKS
+
 // used for section->flags
 #define SF_SELECTED   1
 #define SF_SUBSEC     2