diff --git a/doc/emacs/trouble.texi b/doc/emacs/trouble.texi
index bd347b0..e049bd1 100644
--- a/doc/emacs/trouble.texi
+++ b/doc/emacs/trouble.texi
@@ -148,6 +148,7 @@ Lossage
 * DEL Does Not Delete::   What to do if @key{DEL} doesn't delete.
 * Stuck Recursive::       '[...]' in mode line around the parentheses.
 * Screen Garbled::        Garbage on the screen.
+* Slow Display::          Slow screen refresh.
 * Text Garbled::          Garbage in the text.
 * Memory Full::           How to cope when you run out of memory.
 * Crashing::              What Emacs does when it crashes.
@@ -247,6 +248,25 @@ Screen Garbled
 entry, it is possible that there is a bug in the terminfo entry, or a
 bug in Emacs that appears for certain terminal types.
 
+@node Slow Display
+@subsection Slow screen refresh
+@cindex display, slow
+@cindex refresh, display slow
+@cindex font, missing
+
+  If the display is too slow in refreshing when you scroll to a new
+region, or when you edit the buffer, it may be due to this that some
+characters cannot be displayed in the default font, and Emacs is
+spending too much time in looking for a suitable font to display them.
+
+  You can suspect this if you have several characters that are
+displayed as small rectangles containing a hexadecimal code inside.
+
+  The solution is to install the appropriate fonts on your
+machine. For instance if you are editing a text with a lot of math
+symbols, then installing a font like @file{Symbola} should solve this
+problem.
+
 @node Text Garbled
 @subsection Garbage in the Text
 @cindex garbled text