diff --git a/src/Makefile b/src/Makefile
index 256eb35..7cdff63 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -73,13 +73,13 @@ gsm.o: gsm.c command.h modem.h gsm.h
 	$(CC) $(phone_CFLAGS) -c gsm.c
 
 main.o: main.c ../include/Phone.h phone.h ../config.h
-	$(CC) $(phone_CFLAGS) -c main.c
+	$(CC) -D PREFIX=\"$(PREFIX)\" $(phone_CFLAGS) -c main.c
 
 modem.o: modem.c gsm.h modem.h
 	$(CC) $(phone_CFLAGS) -c modem.c
 
 phone.o: phone.c ../include/Phone.h phone.h gsm.h callbacks.h ../config.h
-	$(CC) $(phone_CFLAGS) -c phone.c
+	$(CC) -D PREFIX=\"$(PREFIX)\" $(phone_CFLAGS) -c phone.c
 
 contacts.o: contacts.c common.c
 	$(CC) $(phone-contacts_CFLAGS) -c contacts.c
diff --git a/src/project.conf b/src/project.conf
index 8877cff..f89a27e 100644
--- a/src/project.conf
+++ b/src/project.conf
@@ -64,9 +64,11 @@ depends=command.h,modem.h,gsm.h
 
 [main.c]
 depends=../include/Phone.h,phone.h,../config.h
+cppflags=-D PREFIX=\"$(PREFIX)\"
 
 [modem.c]
 depends=gsm.h,modem.h
 
 [phone.c]
 depends=../include/Phone.h,phone.h,gsm.h,callbacks.h,../config.h
+cppflags=-D PREFIX=\"$(PREFIX)\"