--- src/ftfont.c	
+++ src/ftfont.c	
@@ -1262,7 +1262,7 @@ ftfont_open (f, entity, pixel_size)
     spacing = XINT (AREF (entity, FONT_SPACING_INDEX));
   else
     spacing = FC_PROPORTIONAL;
-  if (spacing != FC_PROPORTIONAL)
+  if (spacing != FC_PROPORTIONAL && spacing != FC_DUAL)
     font->min_width = font->average_width = font->space_width
       = (scalable ? ft_face->max_advance_width * size / upEM
 	 : ft_face->size->metrics.max_advance >> 6);
--- src/xftfont.c	
+++ src/xftfont.c	
@@ -418,7 +418,7 @@ xftfont_open (f, entity, pixel_size)
 	ascii_printable[i] = ' ' + i;
     }
   BLOCK_INPUT;
-  if (spacing != FC_PROPORTIONAL)
+  if (spacing != FC_PROPORTIONAL && spacing != FC_DUAL)
     {
       font->min_width = font->average_width = font->space_width
 	= xftfont->max_advance_width;