diff --git a/distr/flecs.c b/distr/flecs.c
index e7f0caddfd..067111a231 100644
--- a/distr/flecs.c
+++ b/distr/flecs.c
@@ -14925,10 +14925,19 @@ void flecs_register_observer_for_id(
     ecs_term_t *term = &o->query->terms[0];
     ecs_entity_t trav = term->trav;
 
-    int i;
+    int i, j;
     for (i = 0; i < o->event_count; i ++) {
         ecs_entity_t event = flecs_get_observer_event(
             term, o->events[i]);
+        for (j = 0; j < i; j ++) {
+            if (event == flecs_get_observer_event(term, o->events[j])) {
+                break;
+            }
+        }
+        if (i != j) {
+            /* Duplicate event, ignore */
+            continue;
+        }
 
         /* Get observers for event */
         ecs_event_record_t *er = flecs_event_record_ensure(observable, event);
@@ -14985,10 +14994,19 @@ void flecs_unregister_observer_for_id(
     ecs_term_t *term = &o->query->terms[0];
     ecs_entity_t trav = term->trav;
 
-    int i;
+    int i, j;
     for (i = 0; i < o->event_count; i ++) {
         ecs_entity_t event = flecs_get_observer_event(
             term, o->events[i]);
+        for (j = 0; j < i; j ++) {
+            if (event == flecs_get_observer_event(term, o->events[j])) {
+                break;
+            }
+        }
+        if (i != j) {
+            /* Duplicate event, ignore */
+            continue;
+        }
 
         /* Get observers for event */
         ecs_event_record_t *er = flecs_event_record_get(observable, event);
diff --git a/src/observer.c b/src/observer.c
index 9851b39db7..8e9b6bf691 100644
--- a/src/observer.c
+++ b/src/observer.c
@@ -130,10 +130,19 @@ void flecs_register_observer_for_id(
     ecs_term_t *term = &o->query->terms[0];
     ecs_entity_t trav = term->trav;
 
-    int i;
+    int i, j;
     for (i = 0; i < o->event_count; i ++) {
         ecs_entity_t event = flecs_get_observer_event(
             term, o->events[i]);
+        for (j = 0; j < i; j ++) {
+            if (event == flecs_get_observer_event(term, o->events[j])) {
+                break;
+            }
+        }
+        if (i != j) {
+            /* Duplicate event, ignore */
+            continue;
+        }
 
         /* Get observers for event */
         ecs_event_record_t *er = flecs_event_record_ensure(observable, event);
@@ -190,10 +199,19 @@ void flecs_unregister_observer_for_id(
     ecs_term_t *term = &o->query->terms[0];
     ecs_entity_t trav = term->trav;
 
-    int i;
+    int i, j;
     for (i = 0; i < o->event_count; i ++) {
         ecs_entity_t event = flecs_get_observer_event(
             term, o->events[i]);
+        for (j = 0; j < i; j ++) {
+            if (event == flecs_get_observer_event(term, o->events[j])) {
+                break;
+            }
+        }
+        if (i != j) {
+            /* Duplicate event, ignore */
+            continue;
+        }
 
         /* Get observers for event */
         ecs_event_record_t *er = flecs_event_record_get(observable, event);
diff --git a/test/core/project.json b/test/core/project.json
index 260f13c038..35f5929962 100644
--- a/test/core/project.json
+++ b/test/core/project.json
@@ -1695,7 +1695,6 @@
                 "forward_up_flag_term_2",
                 "propagate_up_flag_term_1",
                 "propagate_up_flag_term_2",
-                "propagate_on_set_self_up",
                 "row_flag_term_1",
                 "row_flag_term_2",
                 "on_add_optional",
@@ -1712,6 +1711,8 @@
                 "on_table_create_is_deferred",
                 "on_table_create_is_deferred_batched",
                 "2_children_w_deferred_set",
+                "on_add_on_set_w_not_term",
+                "on_add_on_set_w_not_2_terms",
                 "cache_test_1",
                 "cache_test_2",
                 "cache_test_3",
diff --git a/test/core/src/Observer.c b/test/core/src/Observer.c
index 071a663422..1a37df5da3 100644
--- a/test/core/src/Observer.c
+++ b/test/core/src/Observer.c
@@ -9975,3 +9975,88 @@ void Observer_2_children_w_deferred_set(void) {
 
     ecs_fini(world);
 }
+
+void Observer_on_add_on_set_w_not_term(void) {
+    ecs_world_t *world = ecs_mini();
+
+    ECS_COMPONENT(world, Position);
+
+    Probe ctx = {0};
+
+    ecs_entity_t o = ecs_observer(world, {
+        .query.terms = {{ ecs_id(Position), .oper = EcsNot }},
+        .events = { EcsOnAdd, EcsOnSet },
+        .callback = Observer_w_value_1,
+        .ctx = &ctx
+    });
+
+    ecs_entity_t e = ecs_insert(world, ecs_value(Position, {10, 20}));
+    test_int(ctx.invoked, 0);
+
+    ecs_remove(world, e, Position);
+    test_int(ctx.invoked, 1);
+    test_int(ctx.count, 1);
+    test_int(ctx.system, o);
+    test_int(ctx.event, EcsOnAdd);
+    test_uint(ctx.e[0], e);
+    test_uint(ctx.s[0][0], 0);
+
+    ecs_fini(world);
+}
+
+void Observer_on_add_on_set_w_not_2_terms(void) {
+    ecs_world_t *world = ecs_mini();
+
+    ECS_COMPONENT(world, Position);
+    ECS_COMPONENT(world, Velocity);
+
+    Probe ctx = {0};
+
+    ecs_entity_t o = ecs_observer(world, {
+        .query.terms = {{ ecs_id(Position) }, { ecs_id(Velocity), .oper = EcsNot }},
+        .events = { EcsOnAdd, EcsOnSet },
+        .callback = Observer,
+        .ctx = &ctx
+    });
+
+    ecs_entity_t e = ecs_new_w(world, Position);
+    test_int(ctx.invoked, 1);
+    test_int(ctx.count, 1);
+    test_int(ctx.system, o);
+    test_int(ctx.event, EcsOnAdd);
+    test_uint(ctx.e[0], e);
+    test_uint(ctx.s[0][0], 0);
+
+    ecs_os_zeromem(&ctx);
+
+    ecs_set(world, e, Position, {10, 20});
+    test_int(ctx.invoked, 1);
+    test_int(ctx.count, 1);
+    test_int(ctx.system, o);
+    test_int(ctx.event, EcsOnSet);
+    test_uint(ctx.e[0], e);
+    test_uint(ctx.s[0][0], 0);
+
+    ecs_os_zeromem(&ctx);
+
+    ecs_add(world, e, Velocity);
+    test_int(ctx.invoked, 0);
+
+    ecs_set(world, e, Position, {20, 30});
+    test_int(ctx.invoked, 0);
+
+    ecs_remove(world, e, Velocity);
+    test_int(ctx.invoked, 1);
+    test_int(ctx.count, 1);
+    test_int(ctx.system, o);
+    test_int(ctx.event, EcsOnAdd);
+    test_uint(ctx.e[0], e);
+    test_uint(ctx.s[0][0], 0);
+
+    ecs_os_zeromem(&ctx);
+
+    ecs_remove(world, e, Position);
+    test_int(ctx.invoked, 0);
+
+    ecs_fini(world);
+}
diff --git a/test/core/src/main.c b/test/core/src/main.c
index 90e304f1a7..5d50cfd50c 100644
--- a/test/core/src/main.c
+++ b/test/core/src/main.c
@@ -1650,6 +1650,8 @@ void Observer_on_table_create(void);
 void Observer_on_table_create_is_deferred(void);
 void Observer_on_table_create_is_deferred_batched(void);
 void Observer_2_children_w_deferred_set(void);
+void Observer_on_add_on_set_w_not_term(void);
+void Observer_on_add_on_set_w_not_2_terms(void);
 void Observer_cache_test_1(void);
 void Observer_cache_test_2(void);
 void Observer_cache_test_3(void);
@@ -8754,6 +8756,14 @@ bake_test_case Observer_testcases[] = {
         "2_children_w_deferred_set",
         Observer_2_children_w_deferred_set
     },
+    {
+        "on_add_on_set_w_not_term",
+        Observer_on_add_on_set_w_not_term
+    },
+    {
+        "on_add_on_set_w_not_2_terms",
+        Observer_on_add_on_set_w_not_2_terms
+    },
     {
         "cache_test_1",
         Observer_cache_test_1
@@ -11665,7 +11675,7 @@ static bake_test_suite suites[] = {
         "Observer",
         NULL,
         NULL,
-        237,
+        239,
         Observer_testcases
     },
     {