diff --git a/src/osd/sdl/debugqtview.c b/src/osd/sdl/debugqtview.c
index 45432a41269..fdcd4ae43b2 100644
--- a/src/osd/sdl/debugqtview.c
+++ b/src/osd/sdl/debugqtview.c
@@ -32,7 +32,7 @@ void DebuggerView::paintEvent(QPaintEvent* event)
 {
     // Tell the MAME debug view how much real estate is available
     QFontMetrics actualFont = fontMetrics();
-    const int fontWidth = MAX(1, actualFont.maxWidth());
+    const int fontWidth = MAX(1, actualFont.width('_'));
     const int fontHeight = MAX(1, actualFont.height());
     m_view->set_visible_size(debug_view_xy(width()/fontWidth, height()/fontHeight));
 
@@ -206,7 +206,7 @@ void DebuggerView::mousePressEvent(QMouseEvent* event)
 	if (event->button() == Qt::LeftButton)
 	{
 		QFontMetrics actualFont = fontMetrics();
-		const int fontWidth = MAX(1, actualFont.maxWidth());
+		const int fontWidth = MAX(1, actualFont.width('_'));
 		const int fontHeight = MAX(1, actualFont.height());
 		
 		debug_view_xy topLeft = m_view->visible_position();