Index: driver/Makefile.am
===================================================================
--- driver/Makefile.am	(revision a499702f9cb88d11867117e3eaa5e131c8165d5b)
+++ driver/Makefile.am	(revision 7a486f4a7af9fc14277971204736f701763d00a6)
@@ -19,5 +19,5 @@
 
 # applies to both programs
-AM_CXXFLAGS = @HOST_FLAGS@ -Wall -O2 -g -std=c++14 -I${abs_top_srcdir}/src -I${abs_top_srcdir}/src/include
+AM_CXXFLAGS = @HOST_FLAGS@ -Wall -Wextra -Werror=return-type -O2 -g -std=c++14 -I${abs_top_srcdir}/src -I${abs_top_srcdir}/src/include
 
 # don't install cfa directly