diff --git a/nmigen/vendor/xilinx_7series.py b/nmigen/vendor/xilinx_7series.py
index 85a3650..df1b5d8 100644
--- a/nmigen/vendor/xilinx_7series.py
+++ b/nmigen/vendor/xilinx_7series.py
@@ -1,5 +1,15 @@
+import warnings
+
 from .xilinx import XilinxPlatform
 
+
 __all__ = ["Xilinx7SeriesPlatform"]
 
+
 Xilinx7SeriesPlatform = XilinxPlatform
+
+
+# TODO(nmigen-0.4): remove
+warnings.warn("instead of nmigen.vendor.xilinx_7series.Xilinx7SeriesPlatform, "
+              "use nmigen.vendor.xilinx.XilinxPlatform",
+              DeprecationWarning, stacklevel=2)
diff --git a/nmigen/vendor/xilinx_spartan_3_6.py b/nmigen/vendor/xilinx_spartan_3_6.py
index ced94ed..c55905f 100644
--- a/nmigen/vendor/xilinx_spartan_3_6.py
+++ b/nmigen/vendor/xilinx_spartan_3_6.py
@@ -1,6 +1,16 @@
+import warnings
+
 from .xilinx import XilinxPlatform
 
+
 __all__ = ["XilinxSpartan3APlatform", "XilinxSpartan6Platform"]
 
+
 XilinxSpartan3APlatform = XilinxPlatform
 XilinxSpartan6Platform = XilinxPlatform
+
+
+# TODO(nmigen-0.4): remove
+warnings.warn("instead of nmigen.vendor.xilinx_spartan_3_6.XilinxSpartan3APlatform and "
+              ".XilinxSpartan6Platform, use nmigen.vendor.xilinx.XilinxPlatform",
+              DeprecationWarning, stacklevel=2)
diff --git a/nmigen/vendor/xilinx_ultrascale.py b/nmigen/vendor/xilinx_ultrascale.py
index 92aace0..ead8d93 100644
--- a/nmigen/vendor/xilinx_ultrascale.py
+++ b/nmigen/vendor/xilinx_ultrascale.py
@@ -1,5 +1,15 @@
+import warnings
+
 from .xilinx import XilinxPlatform
 
+
 __all__ = ["XilinxUltraScalePlatform"]
 
+
 XilinxUltraScalePlatform = XilinxPlatform
+
+
+# TODO(nmigen-0.4): remove
+warnings.warn("instead of nmigen.vendor.xilinx_ultrascale.XilinxUltraScalePlatform, "
+              "use nmigen.vendor.xilinx.XilinxPlatform",
+              DeprecationWarning, stacklevel=2)