diff --git a/litedram/frontend/wishbone.py b/litedram/frontend/wishbone.py
index 251d28e..42288f8 100644
--- a/litedram/frontend/wishbone.py
+++ b/litedram/frontend/wishbone.py
@@ -8,7 +8,7 @@ from migen import *

 class LiteDRAMWishbone2Native(Module):
     def __init__(self, wishbone, port):
-        assert len(wishbone.dat_w) == len(port.wdata.data)
+        assert len(wishbone.dat_w) == len(port.wdata.data), "%r vs. %r" % (len(wishbone.dat_w), len(port.wdata.data))

         # # #

@@ -54,7 +54,7 @@ class LiteDRAMWishbone2Native(Module):

 class LiteDRAMWishbone2AXI(Module):
     def __init__(self, wishbone, port):
-        assert len(wishbone.dat_w) == len(port.w.data)
+        assert len(wishbone.dat_w) == len(port.w.data), "%r vs. %r" % (len(wishbone.dat_w), len(port.w.data))

         # # #