diff --git a/litex/build/generic_toolchain.py b/litex/build/generic_toolchain.py
index 488b92178..fd1c0af37 100644
--- a/litex/build/generic_toolchain.py
+++ b/litex/build/generic_toolchain.py
@@ -8,7 +8,7 @@
 import os
 import math
 
-from migen.fhdl.structure import _Fragment
+from migen.fhdl.structure import Signal, _Fragment
 
 from litex.gen import LiteXContext
 
@@ -178,7 +178,9 @@ class GenericToolchain:
 
     def add_false_path_constraint(self, platform, from_, to, keep=True):
         if keep:
-            from_.attr.add("keep")
-            to.attr.add("keep")
+            if isinstance(from_, Signal):
+                from_.attr.add("keep")
+            if isinstance(to, Signal):
+                to.attr.add("keep")
         if (to, from_) not in self.false_paths:
             self.false_paths.add((from_, to))