diff --git a/dumux/io/plotmateriallaw.hh b/dumux/io/plotmateriallaw.hh
index 92488748d5c28cca2f29f880ab747e8baf84a772..cf2ff58006ef61d1f759481b0ee7649edb34fb8d 100644
--- a/dumux/io/plotmateriallaw.hh
+++ b/dumux/io/plotmateriallaw.hh
@@ -24,6 +24,8 @@
 #ifndef DUMUX_PLOT_FLUID_MATRIX_LAW_HH
 #define DUMUX_PLOT_FLUID_MATRIX_LAW_HH
 
+#warning "This header is deprecated and will be removed after 3.3. Use new 2p material laws and plot tools from io/plotpckrsw.hh"
+
 #include <cmath>
 #include <vector>
 #include <string>