Index: driver/Makefile.am
===================================================================
--- driver/Makefile.am	(revision 2a59655a1dd1d977b68a881bb4951a8e017eeb1d)
+++ driver/Makefile.am	(revision d958834bbaca85420da00e8a912914e2702ecacb)
@@ -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