diff --git a/litex/build/io.py b/litex/build/io.py
index af8ecbcba5..8d59660bfb 100644
--- a/litex/build/io.py
+++ b/litex/build/io.py
@@ -84,7 +84,6 @@ def __init__(self, i, o, clk):
 
 class SDRIO(Special):
     def __init__(self, i, o, clk=None):
-        assert len(i) == len(o)
         Special.__init__(self)
         self.i            = wrap(i)
         self.o            = wrap(o)
@@ -92,6 +91,7 @@ def __init__(self, i, o, clk=None):
             clk = ClockSignal()
         self.clk          = wrap(clk)
         self.clk_domain   = None if not hasattr(clk, "cd") else clk.cd
+        assert len(self.i) == len(self.o)
 
     def iter_expressions(self):
         yield self, "i"  , SPECIAL_INPUT
@@ -119,13 +119,13 @@ def __init__(self, io, o, oe, i, clk):
 
 class SDRTristate(Special):
     def __init__(self, io, o, oe, i, clk=None):
-        assert len(i) == len(o) == len(oe)
         Special.__init__(self)
         self.io  = wrap(io)
         self.o   = wrap(o)
         self.oe  = wrap(oe)
         self.i   = wrap(i)
         self.clk = wrap(clk) if clk is not None else ClockSignal()
+        assert len(self.i) == len(self.o) == len(self.oe)
 
     def iter_expressions(self):
         yield self, "io" , SPECIAL_INOUT