diff --git a/src/Makefile b/src/Makefile
index 852e071..a423c0b 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -57,7 +57,7 @@ SCR_TEST_OBJECTS=$(SCR_TEST_SOURCES:.c=.o)
 SCR_TEST_LIBS=-lSDL2 $(LUA_LIBS)
 
 TTY_TEST_EXECUTABLE=tty_test
-TTY_TEST_SOURCES=cpu.c ins.c mem.c fmt.c one.c tty.c pia.c chr.c utl.c tty_test.c lua.c
+TTY_TEST_SOURCES=cpu.c ins.c mem.c fmt.c one.c tty.c pia.c chr.c utl.c tty_test.c lua.c sdl.c
 TTY_TEST_OBJECTS=$(TTY_TEST_SOURCES:.c=.o)
 TTY_TEST_LIBS=-lSDL2 $(LUA_LIBS)