diff --git a/test_keywordset.c b/test_keywordset.c
index 464ae3c0..cbaa401c 100644
--- a/test_keywordset.c
+++ b/test_keywordset.c
@@ -23,6 +23,16 @@ static void test_update(struct keywordset *kws, char *update, char *expect) {
     free(init);
 }
 
+static void test_add(struct keywordset *kws, char *add, char *expect) {
+    char *init = keywordset_get(kws);
+    keywordset_add(kws, add);
+    char *s = keywordset_get(kws);
+    if (strcmp(s, expect))
+        fprintf(stderr, "FAIL: add '%s' with '%s' got '%s' expected '%s'\n", init, add, s, expect);
+    free(s);
+    free(init);
+}
+
 int main() {
 
     test_new(NULL,                               "");
@@ -52,4 +62,9 @@ int main() {
     test_update(kws, "+ab",    "ab abcdef");
     test_update(kws, "+abcdefgh",    "ab abcdef abcdefgh");
     keywordset_free(kws);
+
+    kws = keywordset_new("x x x");
+    test_add(kws, "a b c", "a b c x");
+    test_add(kws, "-x +y", "+y -x a b c x");
+    keywordset_free(kws);
 }