Index: libcfa/src/Makefile.am
===================================================================
--- libcfa/src/Makefile.am	(revision 12b5e94a9df5bfc0037b0fe7eb823f658a9b0d9d)
+++ libcfa/src/Makefile.am	(revision 454b4e01b75e00e1a232a34fc6777a3e01b733c2)
@@ -33,6 +33,6 @@
 # The built sources must not depend on the installed inst_headers_src
 AM_CFAFLAGS = -quiet -cfalib -I$(srcdir)/stdhdr -I$(srcdir)/concurrency $(if $(findstring ${gdbwaittarget}, ${@}), -XCFA --gdb) @CONFIG_CFAFLAGS@
-AM_CFLAGS = -g -Wall -Wno-unused-function -fPIC -fexceptions -pthread @ARCH_FLAGS@ @CONFIG_CFLAGS@
-AM_CCASFLAGS = -g -Wall -Wno-unused-function @ARCH_FLAGS@ @CONFIG_CFLAGS@
+AM_CFLAGS = -g -Wall -Werror=return-type -Wno-unused-function -fPIC -fexceptions -pthread @ARCH_FLAGS@ @CONFIG_CFLAGS@
+AM_CCASFLAGS = -g -Wall -Werror=return-type -Wno-unused-function @ARCH_FLAGS@ @CONFIG_CFLAGS@
 CFACC = @CFACC@
 
Index: libcfa/src/concurrency/io/setup.cfa
===================================================================
--- libcfa/src/concurrency/io/setup.cfa	(revision 12b5e94a9df5bfc0037b0fe7eb823f658a9b0d9d)
+++ libcfa/src/concurrency/io/setup.cfa	(revision 454b4e01b75e00e1a232a34fc6777a3e01b733c2)
@@ -32,5 +32,5 @@
 
 	void __cfa_io_start( processor * proc ) {}
-	bool __cfa_io_flush( processor * proc, int ) {}
+	bool __cfa_io_flush( processor * proc, int ) { return false; }
 	void __cfa_io_stop ( processor * proc ) {}