diff --git a/src/mac/carbon/window.cpp b/src/mac/carbon/window.cpp
index 26c54353c6..b2ca1df78f 100644
--- a/src/mac/carbon/window.cpp
+++ b/src/mac/carbon/window.cpp
@@ -391,9 +391,9 @@ void wxWindowMac::DoScreenToClient(int *x, int *y) const
 
     MacRootWindowToWindow( x , y ) ;
     if ( x )
-            x -= MacGetLeftBorderSize() ;
+            (*x) -= MacGetLeftBorderSize() ;
     if ( y )
-            y -= MacGetTopBorderSize() ;
+            (*y) -= MacGetTopBorderSize() ;
 }
 
 void wxWindowMac::DoClientToScreen(int *x, int *y) const
@@ -401,9 +401,9 @@ void wxWindowMac::DoClientToScreen(int *x, int *y) const
     WindowRef window = (WindowRef) MacGetRootWindow() ;
 
     if ( x )
-            x += MacGetLeftBorderSize() ;
+            (*x) += MacGetLeftBorderSize() ;
     if ( y )
-            y += MacGetTopBorderSize() ;
+            (*y) += MacGetTopBorderSize() ;
 
     MacWindowToRootWindow( x , y ) ;
 
diff --git a/src/mac/window.cpp b/src/mac/window.cpp
index 26c54353c6..b2ca1df78f 100644
--- a/src/mac/window.cpp
+++ b/src/mac/window.cpp
@@ -391,9 +391,9 @@ void wxWindowMac::DoScreenToClient(int *x, int *y) const
 
     MacRootWindowToWindow( x , y ) ;
     if ( x )
-            x -= MacGetLeftBorderSize() ;
+            (*x) -= MacGetLeftBorderSize() ;
     if ( y )
-            y -= MacGetTopBorderSize() ;
+            (*y) -= MacGetTopBorderSize() ;
 }
 
 void wxWindowMac::DoClientToScreen(int *x, int *y) const
@@ -401,9 +401,9 @@ void wxWindowMac::DoClientToScreen(int *x, int *y) const
     WindowRef window = (WindowRef) MacGetRootWindow() ;
 
     if ( x )
-            x += MacGetLeftBorderSize() ;
+            (*x) += MacGetLeftBorderSize() ;
     if ( y )
-            y += MacGetTopBorderSize() ;
+            (*y) += MacGetTopBorderSize() ;
 
     MacWindowToRootWindow( x , y ) ;