--- gcc/ada/libgnat/a-strfix.adb
+++ gcc/ada/libgnat/a-strfix.adb
@@ -192,7 +192,15 @@ package body Ada.Strings.Fixed is
       elsif From not in Source'Range
         or else Through > Source'Last
       then
-         raise Index_Error;
+         --  In most cases this raises an exception, but the case of deleting
+         --  a null string at the end of the current one is a special-case, and
+         --  reflects the equivalence with Replace_String (RM A.4.3 (86/3)).
+
+         if From = Source'Last + 1 and then From = Through then
+            return Source;
+         else
+            raise Index_Error;
+         end if;
 
       else
          declare

--- /dev/null
new file mode 100644
+++ gcc/testsuite/gnat.dg/fixed_delete.adb
@@ -0,0 +1,17 @@
+--  { dg-do run }
+
+with Ada.Text_IO; use Ada.Text_IO;
+with Ada.Strings.Fixed; use Ada.Strings.Fixed;
+
+procedure Fixed_Delete is
+   Str  : String := "a";
+   Str1 : String := Replace_Slice (Str, 2, 2, "");
+   Str2 : String := Delete (Str, 2, 2);
+begin
+   if Str1 /= "a" then
+      raise Program_Error;
+   end if;
+   if Str2 /= "a" then
+      raise Program_Error;
+   end if;
+end Fixed_Delete;