diff --git a/libs/spandsp/src/Makefile.am b/libs/spandsp/src/Makefile.am
index 847900c5b6..85b28a6de2 100644
--- a/libs/spandsp/src/Makefile.am
+++ b/libs/spandsp/src/Makefile.am
@@ -291,7 +291,7 @@ make_at_dictionary$(EXEEXT): $(top_srcdir)/src/make_at_dictionary.c
 	$(CC_FOR_BUILD) -o make_at_dictionary$(EXEEXT) $(top_srcdir)/src/make_at_dictionary.c  -DHAVE_CONFIG_H 
 
 make_modem_filter$(EXEEXT): $(top_srcdir)/src/make_modem_filter.c $(top_srcdir)/src/filter_tools.c 
-	$(CC_FOR_BUILD) -o make_modem_filter$(EXEEXT) $(top_srcdir)/src/make_modem_filter.c $(top_srcdir)/src/filter_tools.c -DHAVE_CONFIG_H
+	$(CC_FOR_BUILD) -o make_modem_filter$(EXEEXT) $(top_srcdir)/src/make_modem_filter.c $(top_srcdir)/src/filter_tools.c -DHAVE_CONFIG_H -lm
 
 # We need to run make_at_dictionary, so it generates the
 # at_interpreter_dictionary.h file