diff --git a/posthog/src/main/java/com/posthog/java/PostHog.java b/posthog/src/main/java/com/posthog/java/PostHog.java
index 281827a..5b4191f 100644
--- a/posthog/src/main/java/com/posthog/java/PostHog.java
+++ b/posthog/src/main/java/com/posthog/java/PostHog.java
@@ -191,6 +191,7 @@ private JSONObject getEventJson(String event, String distinctId, Map<String, Obj
             eventJson.put("timestamp", Instant.now().toString());
             eventJson.put("distinct_id", distinctId);
             eventJson.put("event", event);
+            eventJson.put("$lib", "posthog-java");
             if (properties != null) {
                 eventJson.put("properties", properties);
             }
diff --git a/posthog/src/test/java/com/posthog/java/PostHogTest.java b/posthog/src/test/java/com/posthog/java/PostHogTest.java
index 3f75e35..daa82a6 100644
--- a/posthog/src/test/java/com/posthog/java/PostHogTest.java
+++ b/posthog/src/test/java/com/posthog/java/PostHogTest.java
@@ -100,6 +100,21 @@ public void testCaptureWithProperties() {
                 + "\"}").isEqualTo(new JSONObject(json, "distinct_id", "event", "properties", "timestamp").toString());
     }
 
+    @Test
+    public void testCaptureIncludesLibProperty() {
+        ph.capture("test id", "test event", new HashMap<String, Object>() {
+            {
+                put("movie_id", 123);
+                put("category", "romcom");
+            }
+        });
+        ph.shutdown();
+        assertEquals(1, sender.calls.size());
+        assertEquals(1, sender.calls.get(0).size());
+        JSONObject json = sender.calls.get(0).get(0);
+        assertThatJson("{\"$lib\":\"posthog-java\"}").isEqualTo(new JSONObject(json, "$lib").toString());
+    }
+
     @Test
     public void testIdentifySimple() {
         ph.identify("test id", new HashMap<String, Object>() {