diff --git a/compiler/x86/aoptx86.pas b/compiler/x86/aoptx86.pas
index 8db48acacc..847efc3044 100644
--- a/compiler/x86/aoptx86.pas
+++ b/compiler/x86/aoptx86.pas
@@ -451,8 +451,13 @@ unit aoptx86;
 {$ifdef x86_64}
          or ((p.opsize=S_Q) and Reg1WriteOverwritesReg2Entirely(NR_RDX,reg))
 {$endif x86_64}
-           )
-          );
+           )) or
+          ((p.opcode = A_CWD) and Reg1WriteOverwritesReg2Entirely(NR_DX,reg)) or
+          ((p.opcode = A_CDQ) and Reg1WriteOverwritesReg2Entirely(NR_EDX,reg)) or
+{$ifdef x86_64}
+          ((p.opcode = A_CQO) and Reg1WriteOverwritesReg2Entirely(NR_RDX,reg)) or
+{$endif x86_64}
+          ((p.opcode = A_CBW) and Reg1WriteOverwritesReg2Entirely(NR_AX,reg) and not(Reg1ReadDependsOnReg2(NR_AL,reg)));
       end;