Change SKIP_GTK to SKIP_GTK2 in configure.
diff --git a/src/screen.c b/src/screen.c
index a62e6ec..3df7f66 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -4348,10 +4348,10 @@
 
 #ifdef FEAT_CONCEAL
 	    if (    wp->w_p_conceal
-		    && (!area_highlighting)
-		    && ((lnum != wp->w_cursor.lnum)
-			|| (curwin != wp) || (wp->w_buffer->b_p_ma == FALSE))
-		    && ((syntax_flags & HL_CONCEAL) != 0))
+		    && !area_highlighting
+		    && (lnum != wp->w_cursor.lnum
+			|| curwin != wp || wp->w_buffer->b_p_ma == FALSE)
+		    && (syntax_flags & HL_CONCEAL) != 0)
 
 	    {
 		char_attr = conceal_attr;