diff --git a/Contrib/ExDLL/exdll_with_unit.dpr b/Contrib/ExDLL/exdll_with_unit.dpr
index a186a637..1eb216ba 100644
--- a/Contrib/ExDLL/exdll_with_unit.dpr
+++ b/Contrib/ExDLL/exdll_with_unit.dpr
@@ -63,11 +63,10 @@ end;
 
 function mynsiscallback(const NSPIM: TNSPIM): Pointer; cdecl;
 begin
-  Result := 0;
+  Result := nil;
   if NSPIM = NSPIM_UNLOAD then
     begin
-      // Note: Cannot use NSISDialog here because g_hwndParent has been destroyed at this point
-      MessageBox(0, PChar('NSPIM_UNLOAD is the final callback, goodbye...'), PChar('mynsiscallback'), MB_OK);
+      NSISDialog(PChar('NSPIM_UNLOAD is the final callback, goodbye...'), PChar('mynsiscallback'), MB_OK);
     end;
 end;
 
diff --git a/Contrib/ExDLL/nsis.pas b/Contrib/ExDLL/nsis.pas
index 6b3c227e..dd76e5d2 100644
--- a/Contrib/ExDLL/nsis.pas
+++ b/Contrib/ExDLL/nsis.pas
@@ -195,8 +195,12 @@ begin
 end;
 
 procedure NSISDialog(const text, caption: string; const buttons: integer);
+var
+  hwndOwner: HWND;
 begin
-  MessageBox(g_hwndParent, PChar(text), PChar(caption), buttons);
+  hwndOwner := g_hwndParent;
+  if not IsWindow(g_hwndParent) then hwndOwner := 0; // g_hwndParent is not valid in NSPIM_[GUI]UNLOAD
+  MessageBox(hwndOwner, PChar(text), PChar(caption), buttons);
 end;
 
 begin
diff --git a/Docs/src/history.but b/Docs/src/history.but
index 46d72ebc..4fe29586 100644
--- a/Docs/src/history.but
+++ b/Docs/src/history.but
@@ -12,6 +12,12 @@ Released on ?, 201?
 
 \S2{} Minor Changes
 
+\b Fixed minor issues in the Pascal NSIS plug-in SDK and removed the extrap global variable
+
+\S1{v3.0b2-cl} Changelog
+
+\S2{} Minor Changes
+
 \b Windows 10 support
 
 \H{v3.0b1} 3.0 Beta 1