diff --git a/Makefile b/Makefile
index d9e51f7..8a15e43 100644
--- a/Makefile
+++ b/Makefile
@@ -1,35 +1,45 @@
-CFLAGS  = -std=c99 -Wall
-LDFLAGS = -lrt -lm
+MODS := io
+
+CPPFLAGS := -I.
+CFLAGS   := -std=c99 -Wall
+LDFLAGS  := -lrt -lm
+
+CFLAGS += $(MODS:%=-DHAVE_MOD_%)
+
+OBJS := rosella.o gc.o builtin.o interp.o reader.o $(MODS:%=mods/mod_%.o)
+DEPS := $(OBJS:%.o=%.d)
+GCNO := $(OBJS:%.o=%.gcno)
+GCDA := $(OBJS:%.o=%.gcda)
 
 ifeq ($(DEBUG),yes)
-CFLAGS += -g
-PROFILE = no
-dummy := $(shell rm -f rosella *.gcda *.gcno *.o)
+  CFLAGS  += -g
+  PROFILE := no
+  dummy   := $(shell rm -f rosella $(OBJS) $(GCDA) $(GCNO))
 else
-CFLAGS += -O3 -DNDEBUG -march=nocona
+  CFLAGS  += -O3 -DNDEBUG -march=nocona
+endif
+
+ifeq ($(PROFILE),yes)
+  CFLAGS  += -fprofile-generate
+  LDFLAGS += -fprofile-generate
+endif
+
+ifneq (,$(wildcard *.gcda mods/*.gcda))
+  CFLAGS += -fprofile-use
+  dummy  := $(shell rm -f rosella $(OBJS))
 endif
 
 all: rosella
-.PHONY: all clean
+depend: $(DEPS)
 
-ifeq ($(PROFILE),yes)
-CFLAGS  += -fprofile-generate
-LDFLAGS += -fprofile-generate
-endif
-
-ifneq (,$(wildcard *.gcda))
-CFLAGS += -fprofile-use
-dummy := $(shell rm -f rosella *.o)
-endif
+.PHONY: all clean depend
 
 clean:
-	-rm -f rosella *.o *.gcda *.gcno
+	-rm -f rosella $(OBJS) $(DEPS) $(GCDA) $(GCNO)
 
-rosella: rosella.o gc.o builtin.o interp.o reader.o io_builtin.o
+%.d: %.c
+	$(CC) $(CPPFLAGS) -MM $< -MF $@ -MT $(<:%.c=%.o) -MT $@
 
-rosella.o: rosella.c gc.h builtin.h interp.h
-gc.o: gc.c gc.h
-builtin.o: builtin.c builtin.h interp.h gc.h
-interp.o: interp.c interp.h gc.h builtin.h
-reader.o: reader.c reader.h gc.h builtin.h
-io_builtin.o: io_builtin.c io_builtin.h builtin.h interp.h gc.h
+rosella: $(OBJS)
+
+-include $(DEPS)
diff --git a/io_builtin.c b/mods/mod_io.c
similarity index 99%
rename from io_builtin.c
rename to mods/mod_io.c
index 3de740d..e1e87db 100644
--- a/io_builtin.c
+++ b/mods/mod_io.c
@@ -13,7 +13,8 @@
 #include "gc.h"
 #include "builtin.h"
 #include "interp.h"
-#include "io_builtin.h"
+
+#include "mod_io.h"
 
 static void bi_posix_open(interp_state_t *state);
 //static void bi_posix_openat(interp_state_t *state);
@@ -24,7 +25,7 @@ static void bi_posix_write(interp_state_t *state);
 static void bi_posix_lseek(interp_state_t *state);
 static void bi_posix_close(interp_state_t *state);
 
-void io_builtin_init(void)
+void mod_io_init(void)
 {
   register_builtin(BI_IO_POSIX_OPEN, make_builtin_fn(bi_posix_open));
   //register_builtin(BI_IO_POSIX_OPENAT, make_builtin_fn(bi_posix_openat));
diff --git a/io_builtin.h b/mods/mod_io.h
similarity index 94%
rename from io_builtin.h
rename to mods/mod_io.h
index 16fdd32..ce04dcd 100644
--- a/io_builtin.h
+++ b/mods/mod_io.h
@@ -16,7 +16,7 @@
 
 #define BI_IO_POSIX_CLOSE  "posix-close"
 
-void io_builtin_init(void);
+void mod_io_init(void);
 
 #endif
 /* vim:set sw=2 expandtab: */
diff --git a/reader.c b/reader.c
index 23a43fa..ab6c560 100644
--- a/reader.c
+++ b/reader.c
@@ -15,6 +15,8 @@
 #include "gc.h"
 #include "builtin.h"
 
+#include "reader.h"
+
 typedef struct reader_state
 {
   FILE *file;
diff --git a/rosella.c b/rosella.c
index c14393c..ba2778d 100644
--- a/rosella.c
+++ b/rosella.c
@@ -11,7 +11,10 @@
 #include "builtin.h"
 #include "interp.h"
 #include "reader.h"
-#include "io_builtin.h"
+
+#ifdef HAVE_MOD_io
+#  include "mods/mod_io.h"
+#endif
 
 static void test_builtins(void);
 static void test_weak_boxes_and_wills(void);
@@ -35,7 +38,10 @@ int main(int argc, char **argv)
   gc_init(256*1024, 1024*1024);
   builtin_init();
   interpreter_init();
-  io_builtin_init();
+
+#ifdef HAVE_MOD_io
+  mod_io_init();
+#endif
 
   if (argc < 2 || (strcmp(argv[1], "-t") == 0) || (strcmp(argv[1], "--test") == 0))
   {