diff --git a/font-src/meta/aesthetics.ptl b/font-src/meta/aesthetics.ptl
index 55ec6c9d4..7dd72fb72 100644
--- a/font-src/meta/aesthetics.ptl
+++ b/font-src/meta/aesthetics.ptl
@@ -215,11 +215,12 @@ export : define [calculateMetrics para] : begin
 		HSwToV]
 
 export : define [setFontMetrics para metrics fm] : begin
-	define [object CAP Descender XH Width] metrics
+	define [object CAP Descender XH Width SymbolMid] metrics
 
 	define leading      : Math.round para.leading
-	define asc          : Math.round : leading * CAP / (CAP - Descender)
-	define desc         : Math.round : leading * Descender / (CAP - Descender)
+	define asc          : Math.round : SymbolMid + leading / 2
+	define desc         : Math.round : SymbolMid - leading / 2
+
 	define descenderPad : Math.round : fallback para.descenderPad 0
 	define winMetricAscenderPad  : Math.round : fallback para.winMetricAscenderPad  0
 	define winMetricDescenderPad : Math.round : fallback para.winMetricDescenderPad 0