diff --git a/libs/freetdm/Makefile.am b/libs/freetdm/Makefile.am
index af26f7f2af..5e804b7505 100644
--- a/libs/freetdm/Makefile.am
+++ b/libs/freetdm/Makefile.am
@@ -49,6 +49,7 @@ if HAVE_SNG_ISDN
 INCS += -I/usr/include/sng_isdn
 endif 
 
+# we needed to separate CFLAGS in FTDM_COMPAT_CFLAGS and FTDM_CFLAGS due to -c99 which causes problems with wanpipe headers
 FTDM_COMPAT_CFLAGS = $(INCS) -DFTDM_CONFIG_DIR=\"@confdir@\" -DFTDM_MOD_DIR=\"$(moddir)\" @COMP_VENDOR_COMPAT_CFLAGS@ @DEFS@
 FTDM_CFLAGS = $(INCS) -DFTDM_CONFIG_DIR=\"@confdir@\" -DFTDM_MOD_DIR=\"$(moddir)\" @COMP_VENDOR_CFLAGS@ @DEFS@
 COMPILE   = $(CC) $(FTDM_CFLAGS)
@@ -183,8 +184,8 @@ ftmod_analog_em_la_LIBADD  = libfreetdm.la
 if HAVE_LIBSANGOMA
 mod_LTLIBRARIES += ftmod_wanpipe.la
 ftmod_wanpipe_la_SOURCES = $(SRC)/ftmod/ftmod_wanpipe/ftmod_wanpipe.c
-#some structures within Wanpipe drivers are not c99 compatible, so we need to compile ftmod_wanpipe
-#without c99 flags
+# some structures within Wanpipe drivers are not c99 compatible, so we need to compile ftmod_wanpipe
+# without c99 flags, use FTDM_COMPAT_CFLAGS instead
 ftmod_wanpipe_la_CFLAGS  = $(AM_CFLAGS) $(FTDM_COMPAT_CFLAGS) -D__LINUX__ -I/usr/include/wanpipe
 ftmod_wanpipe_la_LDFLAGS = -shared -module -avoid-version -lsangoma
 ftmod_wanpipe_la_LIBADD  = libfreetdm.la
diff --git a/libs/freetdm/configure.ac b/libs/freetdm/configure.ac
index 592dfd82a3..e26f10b0b2 100644
--- a/libs/freetdm/configure.ac
+++ b/libs/freetdm/configure.ac
@@ -82,7 +82,7 @@ sun)
 	fi
 	;;
 *)
-	COMP_VENDOR_COMPAT_CFLAGS="-Wall -Wunused-variable -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes"
+	COMP_VENDOR_COMPAT_CFLAGS="-Wall -Werror -Wunused-variable -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes"
 	COMP_VENDOR_CFLAGS="-std=c99 $COMP_VENDOR_COMPAT_CFLAGS"
 	;;
 esac
diff --git a/libs/freetdm/src/ftmod/ftmod_zt/ftmod_zt.c b/libs/freetdm/src/ftmod/ftmod_zt/ftmod_zt.c
index 7320934a49..211bf713b7 100644
--- a/libs/freetdm/src/ftmod/ftmod_zt/ftmod_zt.c
+++ b/libs/freetdm/src/ftmod/ftmod_zt/ftmod_zt.c
@@ -31,7 +31,6 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-
 #include "private/ftdm_core.h"
 #include "ftmod_zt.h"
 
diff --git a/libs/freetdm/src/include/ftdm_os.h b/libs/freetdm/src/include/ftdm_os.h
index 5026bb7236..f3ebee9ea2 100644
--- a/libs/freetdm/src/include/ftdm_os.h
+++ b/libs/freetdm/src/include/ftdm_os.h
@@ -39,9 +39,12 @@
 extern "C" {
 #endif
 
+#if defined(__linux__) && !defined(__USE_BSD)
+#define __USE_BSD
+#endif
+
 #include "ftdm_declare.h"
 #include "ftdm_threadmutex.h"
-
 #include <string.h>
 
 #ifndef __WINDOWS__
diff --git a/libs/freetdm/src/testsangomaboost.c b/libs/freetdm/src/testsangomaboost.c
index 529dbbe5e2..b007fc186b 100644
--- a/libs/freetdm/src/testsangomaboost.c
+++ b/libs/freetdm/src/testsangomaboost.c
@@ -49,12 +49,6 @@
 #include <string.h>
 #include <errno.h>
 
-#if defined(__linux__) && !defined(__USE_BSD)
-#define __USE_BSD
-#endif
-#ifndef WIN32
-#include <unistd.h>
-#endif
 #include "freetdm.h"