diff --git a/Contrib/Modern UI 2/Interface.nsh b/Contrib/Modern UI 2/Interface.nsh
index 4acaa0c7..83e6f50c 100644
--- a/Contrib/Modern UI 2/Interface.nsh	
+++ b/Contrib/Modern UI 2/Interface.nsh	
@@ -69,11 +69,25 @@ Var mui.Button.Back
         !insertmacro MUI_SET MUI_HEADERIMAGE_UNBITMAP_STRETCH ${MUI_HEADERIMAGE_BITMAP_STRETCH}
       !endif
 
+      !if "${MUI_HEADERIMAGE_BITMAP}" == ""
+        !error "Invalid MUI_HEADERIMAGE_BITMAP"
+      !endif
+      !if "${MUI_HEADERIMAGE_UNBITMAP}" == ""
+        !error "Invalid MUI_HEADERIMAGE_UNBITMAP"
+      !endif
+
       !ifdef MUI_HEADERIMAGE_BITMAP_RTL
         !ifndef MUI_HEADERIMAGE_UNBITMAP_RTL
           !define MUI_HEADERIMAGE_UNBITMAP_RTL "${MUI_HEADERIMAGE_BITMAP_RTL}"
           !insertmacro MUI_SET MUI_HEADERIMAGE_UNBITMAP_RTL_STRETCH ${MUI_HEADERIMAGE_BITMAP_RTL_STRETCH}
         !endif
+
+        !if "${MUI_HEADERIMAGE_BITMAP_RTL}" == ""
+          !error "Invalid MUI_HEADERIMAGE_BITMAP_RTL"
+        !endif
+        !if "${MUI_HEADERIMAGE_UNBITMAP_RTL}" == ""
+          !error "Invalid MUI_HEADERIMAGE_UNBITMAP_RTL"
+        !endif
       !endif
 
       !insertmacro MUI_DEFAULT MUI_HEADERIMAGE_UNBITMAP_STRETCH ${MUI_HEADERIMAGE_BITMAP_STRETCH}
diff --git a/Contrib/Modern UI 2/Pages.nsh b/Contrib/Modern UI 2/Pages.nsh
index 58ee96d9..e128189b 100644
--- a/Contrib/Modern UI 2/Pages.nsh	
+++ b/Contrib/Modern UI 2/Pages.nsh	
@@ -49,7 +49,7 @@ Support code for all pages
   
   ;Generate unique ID
   !insertmacro MUI_UNSET MUI_UNIQUEID
-  !define MUI_UNIQUEID ${__LINE__}  
+  !define MUI_UNIQUEID ${__LINE__}
 
 !macroend
 
@@ -295,12 +295,12 @@ Support code for all pages
   ${EndIf}
 
   ${DoWhile} $R2 > $R8 ; ImgH > CtlH
-  IntOp $R1 $R1 - $R3
-  IntOp $R2 $R2 - $R4
+    IntOp $R1 $R1 - $R3
+    IntOp $R2 $R2 - $R4
   ${Loop}
   ${DoWhile} $R2 < $R8 ; ImgH < CtlH
-  IntOp $R1 $R1 + $R3
-  IntOp $R2 $R2 + $R4
+    IntOp $R1 $R1 + $R3
+    IntOp $R2 $R2 + $R4
   ${Loop}
   IntOp $1 $R1 / 10000
   IntOp $2 $R2 / 10000
@@ -312,9 +312,9 @@ Support code for all pages
   ${EndIf}
 
   ${DoWhile} $2 > $8 ; Non-aspect-maintained stretch to make it a pixel perfect match
-  IntOp $2 $2 - 1
-  IntOp $1 $1 - 1
-  ${IfThen} $3 == "*" ${|} IntOp $5 $5 + 1 ${|}
+    IntOp $2 $2 - 1
+    IntOp $1 $1 - 1
+    ${IfThen} $3 == "*" ${|} IntOp $5 $5 + 1 ${|}
   ${Loop}
 
   System::Call 'USER32::SetWindowPos(pr0,p0,ir5,ir6,ir1,ir2,i0x14)'
diff --git a/Contrib/Modern UI 2/Pages/Finish.nsh b/Contrib/Modern UI 2/Pages/Finish.nsh
index 2df261fc..f12c6170 100644
--- a/Contrib/Modern UI 2/Pages/Finish.nsh	
+++ b/Contrib/Modern UI 2/Pages/Finish.nsh	
@@ -71,7 +71,10 @@ Finish page (implemented using nsDialogs)
     !endif
   !endif
 
-  !insertmacro MUI_DEFAULT MUI_${MUI_PAGE_UNINSTALLER_PREFIX}WELCOMEFINISHPAGE_BITMAP "${NSISDIR}\Contrib\Graphics\Wizard\win.bmp"  
+  !insertmacro MUI_DEFAULT MUI_${MUI_PAGE_UNINSTALLER_PREFIX}WELCOMEFINISHPAGE_BITMAP "${NSISDIR}\Contrib\Graphics\Wizard\win.bmp"
+  !if "${MUI_${MUI_PAGE_UNINSTALLER_PREFIX}WELCOMEFINISHPAGE_BITMAP}" == ""
+    !error "Invalid MUI_${MUI_PAGE_UNINSTALLER_PREFIX}WELCOMEFINISHPAGE_BITMAP"
+  !endif
 
 !macroend
 
diff --git a/Contrib/Modern UI 2/Pages/Welcome.nsh b/Contrib/Modern UI 2/Pages/Welcome.nsh
index f50d4261..3c9fe035 100644
--- a/Contrib/Modern UI 2/Pages/Welcome.nsh	
+++ b/Contrib/Modern UI 2/Pages/Welcome.nsh	
@@ -20,10 +20,13 @@ Welcome page (implemented using nsDialogs)
     Var mui.WelcomePage.Title
     Var mui.WelcomePage.Title.Font
     
-    Var mui.WelcomePage.Text    
+    Var mui.WelcomePage.Text
   !endif
   
-  !insertmacro MUI_DEFAULT MUI_${MUI_PAGE_UNINSTALLER_PREFIX}WELCOMEFINISHPAGE_BITMAP "${NSISDIR}\Contrib\Graphics\Wizard\win.bmp"  
+  !insertmacro MUI_DEFAULT MUI_${MUI_PAGE_UNINSTALLER_PREFIX}WELCOMEFINISHPAGE_BITMAP "${NSISDIR}\Contrib\Graphics\Wizard\win.bmp"
+  !if "${MUI_${MUI_PAGE_UNINSTALLER_PREFIX}WELCOMEFINISHPAGE_BITMAP}" == ""
+    !error "Invalid MUI_${MUI_PAGE_UNINSTALLER_PREFIX}WELCOMEFINISHPAGE_BITMAP"
+  !endif
 
 !macroend
 
diff --git a/Contrib/Modern UI/System.nsh b/Contrib/Modern UI/System.nsh
index 872033c6..f5f6fbde 100644
--- a/Contrib/Modern UI/System.nsh	
+++ b/Contrib/Modern UI/System.nsh	
@@ -128,6 +128,12 @@ Var MUI_TEMP2
     !insertmacro MUI_DEFAULT MUI_UNWELCOMEFINISHPAGE_INI "${NSISDIR}\Contrib\Modern UI\ioSpecial.ini"
     !insertmacro MUI_DEFAULT MUI_WELCOMEFINISHPAGE_BITMAP "${NSISDIR}\Contrib\Graphics\Wizard\win.bmp"
     !insertmacro MUI_DEFAULT MUI_UNWELCOMEFINISHPAGE_BITMAP "${NSISDIR}\Contrib\Graphics\Wizard\win.bmp"
+    !if "${MUI_WELCOMEFINISHPAGE_BITMAP}" == ""
+      !error "Invalid MUI_WELCOMEFINISHPAGE_BITMAP"
+    !endif
+    !if "${MUI_UNWELCOMEFINISHPAGE_BITMAP}" == ""
+      !error "Invalid MUI_UNWELCOMEFINISHPAGE_BITMAP"
+    !endif
 
     !ifdef MUI_HEADERIMAGE
 
@@ -140,6 +146,13 @@ Var MUI_TEMP2
         !endif
       !endif
 
+      !if "${MUI_HEADERIMAGE_BITMAP}" == ""
+        !error "Invalid MUI_HEADERIMAGE_BITMAP"
+      !endif
+      !if "${MUI_HEADERIMAGE_UNBITMAP}" == ""
+        !error "Invalid MUI_HEADERIMAGE_UNBITMAP"
+      !endif
+
       !ifdef MUI_HEADERIMAGE_BITMAP_RTL
         !ifndef MUI_HEADERIMAGE_UNBITMAP_RTL
           !define MUI_HEADERIMAGE_UNBITMAP_RTL "${MUI_HEADERIMAGE_BITMAP_RTL}"
@@ -147,6 +160,13 @@ Var MUI_TEMP2
             !insertmacro MUI_SET MUI_HEADERIMAGE_UNBITMAP_RTL_NOSTRETCH
           !endif
         !endif
+
+        !if "${MUI_HEADERIMAGE_BITMAP_RTL}" == ""
+          !error "Invalid MUI_HEADERIMAGE_BITMAP_RTL"
+        !endif
+        !if "${MUI_HEADERIMAGE_UNBITMAP_RTL}" == ""
+          !error "Invalid MUI_HEADERIMAGE_UNBITMAP_RTL"
+        !endif
       !endif
 
     !endif