diff --git a/core/user.go b/core/user.go
index bc69764..11cb969 100644
--- a/core/user.go
+++ b/core/user.go
@@ -224,18 +224,36 @@ func fetchUserWorks(r *http.Request, user *User, id string, category UserWorkCat
 
 	// Fetch frequent tags if requested
 	if getTags {
-		var tagsIDs string
+		var tagsIDs []string
 
 		// TODO: frequent tags for novels are *not* fetched when CategoryAny or CategoryAnyAlt
+
+		// Since category is pre-validated, we don't need to handle unexpected categories
 		if category == CategoryAny || category == CategoryAnyAlt || category == CategoryIllustration || category == CategoryManga {
-			tagsIDs = illustrationIDs + mangaIDs
-		} else {
-			tagsIDs = novelIDs
+			// Append illustrationIDs and mangaIDs if they are not empty
+			if illustrationIDs != "" {
+				tagsIDs = append(tagsIDs, illustrationIDs)
+			}
+			if mangaIDs != "" {
+				tagsIDs = append(tagsIDs, mangaIDs)
+			}
+		} else if category == CategoryNovels {
+			// Append novelIDs if not empty
+			if novelIDs != "" {
+				tagsIDs = append(tagsIDs, novelIDs)
+			}
 		}
 
-		user.FrequentTags, err = getUserFrequentTags(r, tagsIDs, category)
-		if err != nil {
-			return err
+		if len(tagsIDs) == 0 {
+			// No tags to fetch, set FrequentTags to empty slice
+			user.FrequentTags = []FrequentTag{}
+		} else {
+			// Concatenate IDs with commas to form a single string
+			ids := strings.Join(tagsIDs, ",")
+			user.FrequentTags, err = getUserFrequentTags(r, ids, category)
+			if err != nil {
+				return fmt.Errorf("failed to get user frequent tags: %w", err)
+			}
 		}
 	}