diff --git a/gcc/ada/libgnat/a-tiflau.adb b/gcc/ada/libgnat/a-tiflau.adb
index 25d78ca8884..214b5c8f2c3 100644
--- a/gcc/ada/libgnat/a-tiflau.adb
+++ b/gcc/ada/libgnat/a-tiflau.adb
@@ -194,7 +194,7 @@ package body Ada.Text_IO.Float_Aux is
       Aft  : Field;
       Exp  : Field)
    is
-      Buf : String (1 .. 3 * Field'Last + 2);
+      Buf : String (1 .. Max_Real_Image_Length);
       Ptr : Natural := 0;
 
    begin
@@ -212,7 +212,7 @@ package body Ada.Text_IO.Float_Aux is
       Aft  : Field;
       Exp  : Field)
    is
-      Buf : String (1 .. 3 * Field'Last + 2);
+      Buf : String (1 .. Max_Real_Image_Length);
       Ptr : Natural := 0;
 
    begin
diff --git a/gcc/ada/libgnat/s-imgrea.adb b/gcc/ada/libgnat/s-imgrea.adb
index 642724b3af7..68b1fdc6ffd 100644
--- a/gcc/ada/libgnat/s-imgrea.adb
+++ b/gcc/ada/libgnat/s-imgrea.adb
@@ -151,14 +151,9 @@ package body System.Img_Real is
       Scale : Integer;
       Expon : Integer;
 
-      Field_Max : constant := 255;
-      --  This should be the same value as Ada.[Wide_]Text_IO.Field'Last.
-      --  It is not worth dragging in Ada.Text_IO to pick up this value,
-      --  since it really should never be necessary to change it.
-
-      Digs : String (1 .. 2 * Field_Max + 16);
-      --  Array used to hold digits of converted integer value. This is a
-      --  large enough buffer to accommodate ludicrous values of Fore and Aft.
+      Digs : String (1 .. Max_Real_Image_Length);
+      --  Array used to hold digits of converted integer value. This is a large
+      --  enough buffer to accommodate ludicrous Fore/Aft/Exp combinations.
 
       Ndigs : Natural;
       --  Number of digits stored in Digs (and also subscript of last digit)
diff --git a/gcc/ada/libgnat/s-imgrea.ads b/gcc/ada/libgnat/s-imgrea.ads
index 8adb6230645..9711516164c 100644
--- a/gcc/ada/libgnat/s-imgrea.ads
+++ b/gcc/ada/libgnat/s-imgrea.ads
@@ -73,4 +73,9 @@ package System.Img_Real is
    --  can be set to any valid values for the case of use from Text_IO. Note
    --  that no space is stored at the start for non-negative values.
 
+   Max_Real_Image_Length : constant := 5200;
+   --   If Exp is set to zero and Aft is set to Text_IO.Field'Last (i.e., 255)
+   --   then Long_Long_Float'Last generates an image whose length is
+   --   slightly less than 5200.
+
 end System.Img_Real;