Index: src/Makefile.am
===================================================================
--- src/Makefile.am	(revision a554e5f423752296e46ab9ced5a34d32676e55d5)
+++ src/Makefile.am	(revision 850aff17345d3e7433f854ef3f1b65369f8016d8)
@@ -59,5 +59,5 @@
 
 $(srcdir)/AST/Type.hpp : BasicTypes-gen.cc
-	${AM_V_GEN}${CXXCOMPILE} $< -o BasicTypes-gen -Wall -Wextra
+	${AM_V_GEN}${CXXCOMPILE} $< -o BasicTypes-gen -Wall -Wextra -Werror=return-type
 	@./BasicTypes-gen
 	@rm BasicTypes-gen
@@ -71,5 +71,5 @@
 EXTRA_DIST = include/cassert include/optional BasicTypes-gen.cc
 
-AM_CXXFLAGS = @HOST_FLAGS@ -Wno-deprecated -Wall -Wextra -DDEBUG_ALL -I./Parser -I$(srcdir)/Parser -I$(srcdir)/include -DYY_NO_INPUT -O3 -g -std=c++14 $(TCMALLOCFLAG)
+AM_CXXFLAGS = @HOST_FLAGS@ -Wno-deprecated -Wall -Wextra -Werror=return-type -DDEBUG_ALL -I./Parser -I$(srcdir)/Parser -I$(srcdir)/include -DYY_NO_INPUT -O3 -g -std=c++14 $(TCMALLOCFLAG)
 AM_LDFLAGS  = @HOST_FLAGS@ -Xlinker -export-dynamic
 ARFLAGS     = cr