diff --git a/lib/dmon/dmon.h b/lib/dmon/dmon.h
index 496463f1..1a7eed3b 100644
--- a/lib/dmon/dmon.h
+++ b/lib/dmon/dmon.h
@@ -107,7 +107,8 @@ typedef enum dmon_error_enum {
     DMON_ERROR_OPEN_DIR,
     DMON_ERROR_MONITOR_FAIL,
     DMON_ERROR_UNSUPPORTED_SYMLINK,
-    DMON_ERROR_END,
+    DMON_ERROR_SUBDIR_LOCATION,
+    DMON_ERROR_END
 } dmon_error;
 
 #ifdef __cplusplus
@@ -364,6 +365,7 @@ static const char *dmon__errors[] = {
     "Error opening directory",
     "Error enabling monitoring",
     "Error support for symlink disabled",
+    "Error not a subdirectory",
 };
 
 DMON_API_IMPL const char *dmon_error_str(dmon_error err) {
diff --git a/lib/dmon/dmon_extra.h b/lib/dmon/dmon_extra.h
index 9b201e17..2252c88e 100644
--- a/lib/dmon/dmon_extra.h
+++ b/lib/dmon/dmon_extra.h
@@ -27,7 +27,7 @@
 extern "C" {
 #endif
 
-DMON_API_DECL bool dmon_watch_add(dmon_watch_id id, const char* subdir);
+DMON_API_DECL bool dmon_watch_add(dmon_watch_id id, const char* subdir, dmon_error *error_code);
 DMON_API_DECL bool dmon_watch_rm(dmon_watch_id id, const char* watchdir);
 
 #ifdef __cplusplus
@@ -36,7 +36,7 @@ DMON_API_DECL bool dmon_watch_rm(dmon_watch_id id, const char* watchdir);
 
 #ifdef DMON_IMPL
 #if DMON_OS_LINUX
-DMON_API_IMPL bool dmon_watch_add(dmon_watch_id id, const char* watchdir)
+DMON_API_IMPL bool dmon_watch_add(dmon_watch_id id, const char* watchdir, dmon_error *error_code)
 {
     DMON_ASSERT(id.id > 0 && id.id <= DMON_MAX_WATCHES);
 
@@ -64,6 +64,7 @@ DMON_API_IMPL bool dmon_watch_add(dmon_watch_id id, const char* watchdir)
         dmon__strcpy(fullpath, sizeof(fullpath), watch->rootdir);
         dmon__strcat(fullpath, sizeof(fullpath), watchdir);
         if (stat(fullpath, &st) != 0 || (st.st_mode & S_IFDIR) == 0) {
+            *error_code = DMON_ERROR_UNSUPPORTED_SYMLINK;
             if (!skip_lock)
                 pthread_mutex_unlock(&_dmon.mutex);
             return false;
@@ -80,6 +81,7 @@ DMON_API_IMPL bool dmon_watch_add(dmon_watch_id id, const char* watchdir)
     // check that the directory is not already added
     for (int i = 0, c = stb_sb_count(watch->subdirs); i < c; i++) {
         if (strcmp(subdir.rootdir, watch->subdirs[i].rootdir) == 0) {
+            *error_code = DMON_ERROR_SUBDIR_LOCATION;
             if (!skip_lock) 
                 pthread_mutex_unlock(&_dmon.mutex);
             return false;
@@ -92,6 +94,7 @@ DMON_API_IMPL bool dmon_watch_add(dmon_watch_id id, const char* watchdir)
     dmon__strcat(fullpath, sizeof(fullpath), subdir.rootdir);
     int wd = inotify_add_watch(watch->fd, fullpath, inotify_mask);
     if (wd == -1) {
+        *error_code = DMON_ERROR_WATCH_DIR;
         if (!skip_lock)
             pthread_mutex_unlock(&_dmon.mutex);
         return false;
@@ -136,6 +139,7 @@ DMON_API_IMPL bool dmon_watch_rm(dmon_watch_id id, const char* watchdir)
         }
     }
     if (i >= c) {
+        *error_code = DMON_ERROR_SUBDIR_LOCATION;
         if (!skip_lock)
             pthread_mutex_unlock(&_dmon.mutex);
         return false;
diff --git a/src/api/system.c b/src/api/system.c
index 1a862f78..45776b51 100644
--- a/src/api/system.c
+++ b/src/api/system.c
@@ -753,7 +753,14 @@ static int f_watch_dir_add(lua_State *L) {
   dmon_watch_id watch_id;
   watch_id.id = luaL_checkinteger(L, 1);
   const char *subdir = luaL_checkstring(L, 2);
-  lua_pushboolean(L, dmon_watch_add(watch_id, subdir));
+  dmon_error error_code;
+  int success = dmon_watch_add(watch_id, subdir, &error_code)
+  if (!success) {
+    lua_pushboolean(L, 0);
+    lua_pushstring(L, dmon_error_str(error_code));
+    return 2;
+  }
+  lua_pushboolean(L, 1);
   return 1;
 }