diff --git a/modules/sign_extender.sv b/modules/sign_extender.sv
index 1f784ae..e2b9e0e 100644
--- a/modules/sign_extender.sv
+++ b/modules/sign_extender.sv
@@ -7,12 +7,13 @@ module sign_extender #(in_width=4, out_width=5)(
     output logic [2**out_width-1:0] ext_val
 );
     logic [0:0] msb;
-    assign msb = (val && {1'b1, {(in_width-1){1'b0}}}) >> (in_width-1);
+    assign msb = (val >> (in_width-1)) & 1'b1;
     always_comb begin
         if (op) begin
-            ext_val = { {(2**(out_width-in_width)){msb}}, val};
-        end else begin
-            ext_val = ({{(2**(out_width-in_width)){1'b0}}, val});
+            ext_val = { {(2**out_width-2**in_width){msb}}, val};
+        end
+        if (~op) begin
+            ext_val = ({{(2**out_width-2**in_width){1'b0}}, val});
         end
     end
 endmodule