diff --git a/.gitignore b/.gitignore
index 5694e12334..6b9df32295 100644
--- a/.gitignore
+++ b/.gitignore
@@ -85,3 +85,4 @@ test/unit/out/
 
 www/cache/
 __pycache__
+.DS_Store
diff --git a/ChangeLog.txt b/ChangeLog.txt
index 240f4a807a..145f5f8168 100644
--- a/ChangeLog.txt
+++ b/ChangeLog.txt
@@ -1,3 +1,7 @@
+Client library:
+- Add `MOSQ_OPT_DELAYED_ACK` option to delaying the PUBACK message
+  until the on_message callback returns.
+
 2.0.0 - 2020-12-03
 ==================
 
diff --git a/include/mosquitto.h b/include/mosquitto.h
index 6232a606b5..00147cb6d0 100644
--- a/include/mosquitto.h
+++ b/include/mosquitto.h
@@ -131,6 +131,7 @@ enum mosq_opt_t {
 	MOSQ_OPT_TCP_NODELAY = 11,
 	MOSQ_OPT_BIND_ADDRESS = 12,
 	MOSQ_OPT_TLS_USE_OS_CERTS = 13,
+	MOSQ_OPT_DELAYED_ACK = 14,
 };
 
 
@@ -1467,6 +1468,9 @@ libmosq_EXPORT int mosquitto_opts_set(struct mosquitto *mosq, enum mosq_opt_t op
  *	MOSQ_OPT_TLS_USE_OS_CERTS - Set to 1 to instruct the client to load and
  *	          trust OS provided CA certificates for use with TLS connections.
  *	          Set to 0 (the default) to only use manually specified CA certs.
+ *
+ *	MOSQ_OPT_DELAYED_ACK - Set to 1 to instruct the client to acknowledge QoS 1
+ *            messages after the on_message callback is called.
  */
 libmosq_EXPORT int mosquitto_int_option(struct mosquitto *mosq, enum mosq_opt_t option, int value);
 
diff --git a/lib/handle_publish.c b/lib/handle_publish.c
index 31d2dba814..34640a58af 100644
--- a/lib/handle_publish.c
+++ b/lib/handle_publish.c
@@ -135,7 +135,9 @@ int handle__publish(struct mosquitto *mosq)
 			return MOSQ_ERR_SUCCESS;
 		case 1:
 			util__decrement_receive_quota(mosq);
-			rc = send__puback(mosq, mid, 0, NULL);
+			if(!mosq->delayed_ack){
+				rc = send__puback(mosq, mid, 0, NULL);
+			}
 			pthread_mutex_lock(&mosq->callback_mutex);
 			if(mosq->on_message){
 				mosq->in_callback = true;
@@ -148,6 +150,9 @@ int handle__publish(struct mosquitto *mosq)
 				mosq->in_callback = false;
 			}
 			pthread_mutex_unlock(&mosq->callback_mutex);
+			if(mosq->delayed_ack){
+				rc = send__puback(mosq, mid, 0, NULL);
+			}
 			message__cleanup(&message);
 			mosquitto_property_free_all(&properties);
 			return rc;
diff --git a/lib/mosquitto.c b/lib/mosquitto.c
index 52fd30dac5..3640d73f16 100644
--- a/lib/mosquitto.c
+++ b/lib/mosquitto.c
@@ -193,6 +193,7 @@ int mosquitto_reinitialise(struct mosquitto *mosq, const char *id, bool clean_st
 	mosq->reconnect_delay_max = 1;
 	mosq->reconnect_exponential_backoff = false;
 	mosq->threaded = mosq_ts_none;
+	mosq->delayed_ack = false;
 #ifdef WITH_TLS
 	mosq->ssl = NULL;
 	mosq->ssl_ctx = NULL;
diff --git a/lib/mosquitto_internal.h b/lib/mosquitto_internal.h
index 6810dc3231..c20e3b34d6 100644
--- a/lib/mosquitto_internal.h
+++ b/lib/mosquitto_internal.h
@@ -351,6 +351,7 @@ struct mosquitto {
 #ifdef WITH_EPOLL
 	uint32_t events;
 #endif
+	bool delayed_ack;
 };
 
 #define STREMPTY(str) (str[0] == '\0')
diff --git a/lib/options.c b/lib/options.c
index 8fe1007d66..46c2c378a8 100644
--- a/lib/options.c
+++ b/lib/options.c
@@ -486,6 +486,10 @@ int mosquitto_int_option(struct mosquitto *mosq, enum mosq_opt_t option, int val
 			mosq->tcp_nodelay = (bool)value;
 			break;
 
+		case MOSQ_OPT_DELAYED_ACK:
+			mosq->delayed_ack = (bool)value;
+			break;
+
 		default:
 			return MOSQ_ERR_INVAL;
 	}