diff --git a/pdcurses/overlay.c b/pdcurses/overlay.c
index 42475332..b3f808ad 100644
--- a/pdcurses/overlay.c
+++ b/pdcurses/overlay.c
@@ -46,7 +46,7 @@
 
 static int _copy_win(const WINDOW *src_w, WINDOW *dst_w, int src_tr,
                      int src_tc, int src_br, int src_bc, int dst_tr,
-                     int dst_tc, bool overlay)
+                     int dst_tc, bool _overlay)
 {
     int col, line, y1, fc, *minchng, *maxchng;
     chtype *w1ptr, *w2ptr;
@@ -77,7 +77,7 @@ static int _copy_win(const WINDOW *src_w, WINDOW *dst_w, int src_tr,
         for (col = 0; col < xdiff; col++)
         {
             if ((*w1ptr) != (*w2ptr) &&
-                !((*w1ptr & A_CHARTEXT) == ' ' && overlay))
+                !((*w1ptr & A_CHARTEXT) == ' ' && _overlay))
             {
                 *w2ptr = *w1ptr;
 
@@ -181,7 +181,7 @@ int overwrite(const WINDOW *src_w, WINDOW *dst_w)
 }
 
 int copywin(const WINDOW *src_w, WINDOW *dst_w, int src_tr, int src_tc,
-            int dst_tr, int dst_tc, int dst_br, int dst_bc, int overlay)
+            int dst_tr, int dst_tc, int dst_br, int dst_bc, int _overlay)
 {
     int src_end_x, src_end_y;
     int src_rows, src_cols, dst_rows, dst_cols;
@@ -205,5 +205,5 @@ int copywin(const WINDOW *src_w, WINDOW *dst_w, int src_tr, int src_tc,
     src_end_x = src_tc + min_cols;
 
     return _copy_win(src_w, dst_w, src_tr, src_tc, src_end_y, src_end_x,
-                     dst_tr, dst_tc, overlay);
+                     dst_tr, dst_tc, _overlay);
 }