1 files changed, 9 insertions, 1 deletions

diff --git a/src/fns.c b/src/fns.c
index e4252c98ca5..ff40c706edd 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -2169,7 +2169,15 @@ internal_equal (o1, o2, depth)
   switch (XTYPE (o1))
     {
     case Lisp_Float:
-      return (extract_float (o1) == extract_float (o2));
+      {
+        double d1, d2;
+
+        d1 = extract_float (o1);
+        d2 = extract_float (o2);
+        /* If d is a NaN, then d != d. Two NaNs should be `equal' even
+           though they are not =. */
+        return d1 == d2 || (d1 != d1 && d2 != d2);
+      }
 
     case Lisp_Cons:
       if (!internal_equal (XCAR (o1), XCAR (o2), depth + 1))