diff --git a/litex/boards/platforms/arty_s7.py b/litex/boards/platforms/arty_s7.py
index fdec20887..093e1efa7 100644
--- a/litex/boards/platforms/arty_s7.py
+++ b/litex/boards/platforms/arty_s7.py
@@ -27,7 +27,7 @@ _io = [
     ("user_btn", 2, Pins("J16"), IOStandard("LVCMOS33")),
     ("user_btn", 3, Pins("H13"), IOStandard("LVCMOS33")),
 
-    ("clk100", 0, Pins("R2"), IOStandard("LVCMOS33")),
+    ("clk100", 0, Pins("R2"), IOStandard("SSTL135")),
 
     ("cpu_reset", 0, Pins("C18"), IOStandard("LVCMOS33")),