diff --git a/src/character.c b/src/character.c
index 5753e883c32..b16c9fd6b8b 100644
--- a/src/character.c
+++ b/src/character.c
@@ -394,10 +394,14 @@ lisp_string_width (Lisp_Object string, ptrdiff_t from, ptrdiff_t to,
 				 SBYTES (default_font))))
 		{
 		  Lisp_Object font_info = Ffont_info (default_font, Qnil);
-		  font_width = AREF (font_info, 11);
-		  if (font_info <= 0)
-		    font_width = AREF (font_info, 10);
-		}
+                  font_width
+                    = check_integer_range (AREF (font_info, 11),
+                                           INT_MIN, INT_MAX);
+                  if (font_width <= 0)
+                    font_width
+                      = check_integer_range (AREF (font_info, 10),
+                                             INT_MIN, INT_MAX);
+                }
 	    }
 	  thiswidth = (double) pixelwidth / font_width + 0.5;
 	  chars = end - i;