diff --git a/t/Makefile b/t/Makefile
index ea99aefe3..53c3c5e6a 100644
--- a/t/Makefile
+++ b/t/Makefile
@@ -519,10 +519,10 @@ PRELOAD_CFLAGS += -D_GNU_SOURCE -std=c11
 PRELOAD_LIBS += -ldl
 
 tests-preload.so:	tests-preload.c
-	$(CC) $(PRELOAD_CFLAGS) ${CFLAGS_DEFAULT} -o $@ -shared -fPIC $(LDFLAGS_DEFAULT) $< $(PRELOAD_LIBS)
+	$(CC) $(PRELOAD_CFLAGS) ${CFLAGS_DEFAULT} ${CPPFLAGS_DEFAULT} -o $@ -shared -fPIC $(LDFLAGS_DEFAULT) $< $(PRELOAD_LIBS)
 
 time-fudge-preload.so:	time-fudge-preload.c
-	$(CC) $(PRELOAD_CFLAGS) ${CFLAGS_DEFAULT} -o $@ -shared -fPIC $(LDFLAGS_DEFAULT) $< $(PRELOAD_LIBS)
+	$(CC) $(PRELOAD_CFLAGS) ${CFLAGS_DEFAULT} ${CPPFLAGS_DEFAULT} -o $@ -shared -fPIC $(LDFLAGS_DEFAULT) $< $(PRELOAD_LIBS)
 
 spandsp_send_fax_pcm.c:	../lib/spandsp_logging.compat
 spandsp_send_fax_t38.c:	../lib/spandsp_logging.compat