diff --git a/compiler/nadd.pas b/compiler/nadd.pas
index 751fb38449..b5282d3275 100644
--- a/compiler/nadd.pas
+++ b/compiler/nadd.pas
@@ -493,7 +493,7 @@ implementation
         t       , vl, hp: tnode;
         lt,rt   : tnodetype;
         hdef,
-        rd,ld   : tdef;
+        rd,ld   , inttype: tdef;
         rv,lv,v : tconstexprint;
         rvd,lvd : bestreal;
         ws1,ws2 : pcompilerwidestring;
@@ -505,6 +505,7 @@ implementation
         res,
         b       : boolean;
         cr, cl  : Tconstexprint;
+        v2p, c2p, c1p, v1p: pnode;
       begin
         result:=nil;
         l1:=0;
@@ -1255,6 +1256,74 @@ implementation
                     exit;
                   end;
 
+                {
+                  (v1=const1) and (v2=const2)
+                    can be converted into
+                  ((v1 xor const1) or (v2 xor const2))=0
+                }
+                if (nodetype=andn) and
+                   (left.nodetype=equaln) and
+                   (right.nodetype=equaln) and
+                   (not might_have_sideeffects(left)) and
+                   (not might_have_sideeffects(right)) and
+                   (is_constintnode(taddnode(left).left) or is_constintnode(taddnode(left).right) or
+                    is_constpointernode(taddnode(left).left) or is_constpointernode(taddnode(left).right)) and
+                   (is_constintnode(taddnode(right).left) or is_constintnode(taddnode(right).right) or
+                    is_constpointernode(taddnode(right).left) or is_constpointernode(taddnode(right).right)) then
+                   begin
+                     if is_constnode(taddnode(left).left) then
+                       begin
+                         v1p:=@taddnode(left).right;
+                         c1p:=@taddnode(left).left;
+                       end
+                     else
+                       begin
+                         v1p:=@taddnode(left).left;
+                         c1p:=@taddnode(left).right;
+                       end;
+                     if is_constnode(taddnode(right).left) then
+                       begin
+                         v2p:=@taddnode(right).right;
+                         c2p:=@taddnode(right).left;
+                       end
+                     else
+                       begin
+                         v2p:=@taddnode(right).left;
+                         c2p:=@taddnode(right).right;
+                       end;
+                     if v1p^.resultdef.size=v2p^.resultdef.size then
+                       begin
+                         if not(is_integer(v1p^.resultdef)) or not(is_integer(v2p^.resultdef)) then
+                           begin
+                             case v1p^.resultdef.size of
+                               2:
+                                 inttype:=u16inttype;
+                               4:
+                                 inttype:=u32inttype;
+                               8:
+                                 inttype:=u64inttype;
+                               else
+                                 Internalerror(2020060101);
+                             end;
+
+                             result:=caddnode.create_internal(equaln,
+                               caddnode.create_internal(orn,
+                                 caddnode.create_internal(xorn,ctypeconvnode.create_internal(v1p^.getcopy,inttype),
+                                   ctypeconvnode.create_internal(c1p^.getcopy,inttype)),
+                                 caddnode.create_internal(xorn,ctypeconvnode.create_internal(v2p^.getcopy,inttype),
+                                   ctypeconvnode.create_internal(c2p^.getcopy,inttype))
+                               ),
+                               cordconstnode.create(0,inttype,false));
+                           end
+                         else
+                           result:=caddnode.create_internal(equaln,
+                             caddnode.create_internal(orn,
+                               caddnode.create_internal(xorn,v1p^.getcopy,c1p^.getcopy),
+                               caddnode.create_internal(xorn,v2p^.getcopy,c2p^.getcopy)
+                             ),
+                             cordconstnode.create(0,v1p^.resultdef,false));
+                       end;
+                   end;
                 { even when short circuit boolean evaluation is active, this
                   optimization cannot be performed in case the node has
                   side effects, because this can change the result (e.g., in an
diff --git a/compiler/node.pas b/compiler/node.pas
index 2b81f63377..709ec0bc07 100644
--- a/compiler/node.pas
+++ b/compiler/node.pas
@@ -741,7 +741,7 @@ implementation
 
     function is_constpointernode(p : tnode) : boolean;
       begin
-         is_constpointernode:=(p.nodetype=pointerconstn);
+         is_constpointernode:=(p.nodetype in [pointerconstn,niln]);
       end;
 
     function is_conststringnode(p : tnode) : boolean;