diff --git a/GNUmakefile b/GNUmakefile
index 723f438319..3de8a05bf9 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -1,4 +1,4 @@
-AGDA_EXEC?=agda -W error
+AGDA_EXEC?=agda -W error -W noNoEquivWhenSplitting
 FIX_WHITESPACE?=fix-whitespace
 RTS_OPTIONS=+RTS -H3G -RTS
 AGDA=$(AGDA_EXEC) $(RTS_OPTIONS)