diff --git a/tests/simple/peepopt.v b/tests/simple/peepopt.v
index 1bf427897..b4d113dba 100644
--- a/tests/simple/peepopt.v
+++ b/tests/simple/peepopt.v
@@ -11,3 +11,11 @@ wire [3:0] t;
 assign t = i * 3;
 assign o = t / 3;
 endmodule
+
+module peepopt_dffmuxext_signed(input clk, ce, input signed [1:0] i, output reg signed [3:0] o);
+    always @(posedge clk) if (ce) o <= i;
+endmodule
+
+module peepopt_dffmuxext_unsigned(input clk, ce, input [1:0] i, output reg [3:0] o);
+    always @(posedge clk) if (ce) o <= i;
+endmodule