--- gcc/ada/einfo.adb
+++ gcc/ada/einfo.adb
@@ -8083,8 +8083,14 @@ package body Einfo is
 
    function Is_External_State (Id : E) return B is
    begin
+      --  To qualify, the abstract state must appear with option "external" or
+      --  "synchronous" (SPARK RM 7.1.4(8) and (10)).
+
       return
-        Ekind (Id) = E_Abstract_State and then Has_Option (Id, Name_External);
+        Ekind (Id) = E_Abstract_State
+          and then (Has_Option (Id, Name_External)
+                      or else
+                    Has_Option (Id, Name_Synchronous));
    end Is_External_State;
 
    ------------------
@@ -8255,6 +8261,9 @@ package body Einfo is
 
    function Is_Synchronized_State (Id : E) return B is
    begin
+      --  To qualify, the abstract state must appear with simple option
+      --  "synchronous" (SPARK RM 7.1.4(10)).
+
       return
         Ekind (Id) = E_Abstract_State
           and then Has_Option (Id, Name_Synchronous);

--- gcc/ada/einfo.ads
+++ gcc/ada/einfo.ads
@@ -2553,7 +2553,7 @@ package Einfo is
 
 --    Is_External_State (synthesized)
 --       Applies to all entities, true for abstract states that are subject to
---       option External.
+--       option External or Synchronous.
 
 --    Is_Finalized_Transient (Flag252)
 --       Defined in constants, loop parameters of generalized iterators, and

--- gcc/ada/sem_util.adb
+++ gcc/ada/sem_util.adb
@@ -10261,92 +10261,157 @@ package body Sem_Util is
       --------------------------------
 
       function State_Has_Enabled_Property return Boolean is
-         Decl     : constant Node_Id := Parent (Item_Id);
-         Opt      : Node_Id;
-         Opt_Nam  : Node_Id;
-         Prop     : Node_Id;
-         Prop_Nam : Node_Id;
-         Props    : Node_Id;
+         Decl : constant Node_Id := Parent (Item_Id);
 
-      begin
-         --  The declaration of an external abstract state appears as an
-         --  extension aggregate. If this is not the case, properties can never
-         --  be set.
+         procedure Find_Simple_Properties
+           (Has_External    : out Boolean;
+            Has_Synchronous : out Boolean);
+         --  Extract the simple properties associated with declaration Decl
 
-         if Nkind (Decl) /= N_Extension_Aggregate then
-            return False;
-         end if;
+         function Is_Enabled_External_Property return Boolean;
+         --  Determine whether property Property appears within the external
+         --  property list of declaration Decl, and return its status.
 
-         --  When External appears as a simple option, it automatically enables
-         --  all properties.
+         ----------------------------
+         -- Find_Simple_Properties --
+         ----------------------------
 
-         Opt := First (Expressions (Decl));
-         while Present (Opt) loop
-            if Nkind (Opt) = N_Identifier
-              and then Chars (Opt) = Name_External
-            then
-               return True;
-            end if;
+         procedure Find_Simple_Properties
+           (Has_External    : out Boolean;
+            Has_Synchronous : out Boolean)
+         is
+            Opt : Node_Id;
 
-            Next (Opt);
-         end loop;
+         begin
+            --  Assume that none of the properties are available
 
-         --  When External specifies particular properties, inspect those and
-         --  find the desired one (if any).
+            Has_External    := False;
+            Has_Synchronous := False;
 
-         Opt := First (Component_Associations (Decl));
-         while Present (Opt) loop
-            Opt_Nam := First (Choices (Opt));
+            Opt := First (Expressions (Decl));
+            while Present (Opt) loop
+               if Nkind (Opt) = N_Identifier then
+                  if Chars (Opt) = Name_External then
+                     Has_External := True;
 
-            if Nkind (Opt_Nam) = N_Identifier
-              and then Chars (Opt_Nam) = Name_External
-            then
-               Props := Expression (Opt);
+                  elsif Chars (Opt) = Name_Synchronous then
+                     Has_Synchronous := True;
+                  end if;
+               end if;
 
-               --  Multiple properties appear as an aggregate
+               Next (Opt);
+            end loop;
+         end Find_Simple_Properties;
 
-               if Nkind (Props) = N_Aggregate then
+         ----------------------------------
+         -- Is_Enabled_External_Property --
+         ----------------------------------
 
-                  --  Simple property form
+         function Is_Enabled_External_Property return Boolean is
+            Opt      : Node_Id;
+            Opt_Nam  : Node_Id;
+            Prop     : Node_Id;
+            Prop_Nam : Node_Id;
+            Props    : Node_Id;
 
-                  Prop := First (Expressions (Props));
-                  while Present (Prop) loop
-                     if Chars (Prop) = Property then
-                        return True;
-                     end if;
+         begin
+            Opt := First (Component_Associations (Decl));
+            while Present (Opt) loop
+               Opt_Nam := First (Choices (Opt));
 
-                     Next (Prop);
-                  end loop;
+               if Nkind (Opt_Nam) = N_Identifier
+                 and then Chars (Opt_Nam) = Name_External
+               then
+                  Props := Expression (Opt);
 
-                  --  Property with expression form
+                  --  Multiple properties appear as an aggregate
 
-                  Prop := First (Component_Associations (Props));
-                  while Present (Prop) loop
-                     Prop_Nam := First (Choices (Prop));
+                  if Nkind (Props) = N_Aggregate then
 
-                     --  The property can be represented in two ways:
-                     --      others   => <value>
-                     --    <property> => <value>
+                     --  Simple property form
 
-                     if Nkind (Prop_Nam) = N_Others_Choice
-                       or else (Nkind (Prop_Nam) = N_Identifier
-                                 and then Chars (Prop_Nam) = Property)
-                     then
-                        return Is_True (Expr_Value (Expression (Prop)));
-                     end if;
+                     Prop := First (Expressions (Props));
+                     while Present (Prop) loop
+                        if Chars (Prop) = Property then
+                           return True;
+                        end if;
 
-                     Next (Prop);
-                  end loop;
+                        Next (Prop);
+                     end loop;
 
-               --  Single property
+                     --  Property with expression form
 
-               else
-                  return Chars (Props) = Property;
+                     Prop := First (Component_Associations (Props));
+                     while Present (Prop) loop
+                        Prop_Nam := First (Choices (Prop));
+
+                        --  The property can be represented in two ways:
+                        --      others   => <value>
+                        --    <property> => <value>
+
+                        if Nkind (Prop_Nam) = N_Others_Choice
+                          or else (Nkind (Prop_Nam) = N_Identifier
+                                    and then Chars (Prop_Nam) = Property)
+                        then
+                           return Is_True (Expr_Value (Expression (Prop)));
+                        end if;
+
+                        Next (Prop);
+                     end loop;
+
+                  --  Single property
+
+                  else
+                     return Chars (Props) = Property;
+                  end if;
                end if;
-            end if;
 
-            Next (Opt);
-         end loop;
+               Next (Opt);
+            end loop;
+
+            return False;
+         end Is_Enabled_External_Property;
+
+         --  Local variables
+
+         Has_External    : Boolean;
+         Has_Synchronous : Boolean;
+
+      --  Start of processing for State_Has_Enabled_Property
+
+      begin
+         --  The declaration of an external abstract state appears as an
+         --  extension aggregate. If this is not the case, properties can
+         --  never be set.
+
+         if Nkind (Decl) /= N_Extension_Aggregate then
+            return False;
+         end if;
+
+         Find_Simple_Properties (Has_External, Has_Synchronous);
+
+         --  Simple option External enables all properties (SPARK RM 7.1.2(2))
+
+         if Has_External then
+            return True;
+
+         --  Option External may enable or disable specific properties
+
+         elsif Is_Enabled_External_Property then
+            return True;
+
+         --  Simple option Synchronous
+         --
+         --    enables                disables
+         --       Asynch_Readers         Effective_Reads
+         --       Asynch_Writers         Effective_Writes
+         --
+         --  Note that both forms of External have higher precedence than
+         --  Synchronous (SPARK RM 7.1.4(10)).
+
+         elsif Has_Synchronous then
+            return Nam_In (Property, Name_Async_Readers, Name_Async_Writers);
+         end if;
 
          return False;
       end State_Has_Enabled_Property;

--- /dev/null
new file mode 100644
+++ gcc/testsuite/gnat.dg/sync2.adb
@@ -0,0 +1,27 @@
+--  { dg-do compile }
+
+package body Sync2 with
+  SPARK_Mode,
+  Refined_State => (State => (A, P, T))
+is
+   A : Integer := 0 with Atomic, Async_Readers, Async_Writers;
+
+   protected type Prot_Typ is
+   private
+      Comp : Natural := 0;
+   end Prot_Typ;
+
+   P : Prot_Typ;
+
+   task type Task_Typ;
+
+   T : Task_Typ;
+
+   protected body Prot_Typ is
+   end Prot_Typ;
+
+   task body Task_Typ is
+   begin
+      null;
+   end Task_Typ;
+end Sync2;

--- /dev/null
new file mode 100644
+++ gcc/testsuite/gnat.dg/sync2.ads
@@ -0,0 +1,6 @@
+package Sync2 with
+  SPARK_Mode,
+  Abstract_State => (State with Synchronous)
+is
+   pragma Elaborate_Body;
+end Sync2;

