diff --git a/gcc/ada/ChangeLog b/gcc/ada/ChangeLog
index 4c6dd1fa1ec..39deb156fc2 100644
--- a/gcc/ada/ChangeLog
+++ b/gcc/ada/ChangeLog
@@ -1,3 +1,8 @@
+2018-05-25  Nicolas Roche  <roche@adacore.com>
+
+	* libgnat/s-valrea.adb (Scan_Real): Abort computation once it is sure
+	that the result will be either -infinite or +infinite.
+
 2018-05-25  Patrick Bernardi  <bernardi@adacore.com>
 
 	* libgnat/s-parame.ads, libgnat/s-parame__vxworks.ads,
diff --git a/gcc/ada/libgnat/s-valrea.adb b/gcc/ada/libgnat/s-valrea.adb
index 70f21aafaec..7bc7fd80afe 100644
--- a/gcc/ada/libgnat/s-valrea.adb
+++ b/gcc/ada/libgnat/s-valrea.adb
@@ -342,7 +342,7 @@ package body System.Val_Real is
       --  For base 10, use power of ten table, repeatedly if necessary
 
       elsif Scale > 0 then
-         while Scale > Maxpow loop
+         while Scale > Maxpow and then Uval'Valid loop
             Uval := Uval * Powten (Maxpow);
             Scale := Scale - Maxpow;
          end loop;
@@ -350,18 +350,21 @@ package body System.Val_Real is
          --  Note that we still know that Scale > 0, since the loop
          --  above leaves Scale in the range 1 .. Maxpow.
 
-         Uval := Uval * Powten (Scale);
+         if Uval'Valid then
+            Uval := Uval * Powten (Scale);
+         end if;
 
       elsif Scale < 0 then
-         while (-Scale) > Maxpow loop
+         while (-Scale) > Maxpow and then Uval'Valid loop
             Uval := Uval / Powten (Maxpow);
             Scale := Scale + Maxpow;
          end loop;
 
          --  Note that we still know that Scale < 0, since the loop
          --  above leaves Scale in the range -Maxpow .. -1.
-
-         Uval := Uval / Powten (-Scale);
+         if Uval'Valid then
+            Uval := Uval / Powten (-Scale);
+         end if;
       end if;
 
       --  Here is where we check for a bad based number