diff --git a/include/picrin.h b/include/picrin.h
index 7f029fcf..e2d938e1 100644
--- a/include/picrin.h
+++ b/include/picrin.h
@@ -212,8 +212,8 @@ void pic_warn(pic_state *, const char *);
 
 const char *pic_errmsg(pic_state *);
 
-void pic_debug(pic_state *, pic_value);
-void pic_fdebug(pic_state *, pic_value, XFILE *);
+pic_value pic_debug(pic_state *, pic_value);
+pic_value pic_fdebug(pic_state *, pic_value, XFILE *);
 
 #if defined(__cplusplus)
 }
diff --git a/src/write.c b/src/write.c
index 4925d52a..e96cf706 100644
--- a/src/write.c
+++ b/src/write.c
@@ -154,17 +154,18 @@ write(pic_state *pic, pic_value obj, XFILE *file)
   }
 }
 
-void
+pic_value
 pic_debug(pic_state *pic, pic_value obj)
 {
-  pic_fdebug(pic, obj, xstdout);
+  return pic_fdebug(pic, obj, xstdout);
 }
 
-void
+pic_value
 pic_fdebug(pic_state *pic, pic_value obj, XFILE *file)
 {
   write(pic, obj, file);
   xfflush(file);
+  return obj;
 }
 
 static pic_value