diff --git a/tests/test_i304_regulates.py b/tests/test_i304_regulates.py
new file mode 100644
index 0000000..1ea0389
--- /dev/null
+++ b/tests/test_i304_regulates.py
@@ -0,0 +1,15 @@
+from goatools.gosubdag.gosubdag import GoSubDag
+from goatools.obo_parser import GODag
+
+
+def test_i304_regulates():
+    godag = GODag("go-basic.obo", optional_attrs=["relationship"])
+    optional_relationships = {
+        "regulates",
+        "negatively_regulates",
+        "positively_regulates",
+    }
+    anc = GoSubDag(
+        ["GO:0019222"], godag, optional_relationships, prt=None
+    ).rcntobj.go2ancestors["GO:0019222"]
+    assert len(anc) == 4