diff --git a/winsup/cygserver/Makefile.in b/winsup/cygserver/Makefile.in
index 16a2ccc15..bbdfc25fb 100644
--- a/winsup/cygserver/Makefile.in
+++ b/winsup/cygserver/Makefile.in
@@ -16,7 +16,7 @@ export CXX:=@CXX@
 
 CFLAGS:=@CFLAGS@
 override CXXFLAGS=@CXXFLAGS@
-override CXXFLAGS+=-MMD -D__OUTSIDE_CYGWIN__ -DSYSCONFDIR="\"$(sysconfdir)\""
+override CXXFLAGS+=-MMD -Wimplicit-fallthrough=4 -Werror -D__OUTSIDE_CYGWIN__ -DSYSCONFDIR="\"$(sysconfdir)\""
 
 include ${srcdir}/../Makefile.common