diff --git a/litex/build/xilinx/platform.py b/litex/build/xilinx/platform.py
index 8a167b761..fd75dae1d 100644
--- a/litex/build/xilinx/platform.py
+++ b/litex/build/xilinx/platform.py
@@ -84,11 +84,11 @@ class XilinxPlatform(GenericPlatform):
     def build(self, *args, **kwargs):
         return self.toolchain.build(self, *args, **kwargs)
 
-    def add_period_constraint(self, clk, period):
+    def add_period_constraint(self, clk, period, keep=True):
         if clk is None: return
         if hasattr(clk, "p"):
             clk = clk.p
-        self.toolchain.add_period_constraint(self, clk, period)
+        self.toolchain.add_period_constraint(self, clk, period, keep=keep)
 
     def add_false_path_constraint(self, from_, to):
         if hasattr(from_, "p"):
diff --git a/litex/build/xilinx/vivado.py b/litex/build/xilinx/vivado.py
index ff99eed2f..40f96b85a 100644
--- a/litex/build/xilinx/vivado.py
+++ b/litex/build/xilinx/vivado.py
@@ -386,7 +386,6 @@ class XilinxVivadoToolchain(GenericToolchain):
         if tools.subprocess_call_filtered(shell + [script], common.colors) != 0:
             raise OSError("Error occured during Vivado's script execution.")
 
-
 def vivado_build_args(parser):
     toolchain_group = parser.add_argument_group(title="Vivado toolchain options")
     toolchain_group.add_argument("--synth-mode",                           default="vivado",  help="Synthesis mode (vivado or yosys).")