diff --git a/libi2pd/SSU2Session.cpp b/libi2pd/SSU2Session.cpp
index f2b002cd..46acf05b 100644
--- a/libi2pd/SSU2Session.cpp
+++ b/libi2pd/SSU2Session.cpp
@@ -1661,7 +1661,7 @@ namespace transport
 		// ranges
 		len -= 5;
 		const uint8_t * ranges = buf + 5;
-		while (len > 0 && firstPacketNum)
+		while (len > 0 && firstPacketNum && ackThrough - firstPacketNum < SSU2_MAX_NUM_ACK_PACKETS)
 		{
 			uint32_t lastPacketNum = firstPacketNum - 1;
 			if (*ranges > lastPacketNum) break;
diff --git a/libi2pd/SSU2Session.h b/libi2pd/SSU2Session.h
index 363cb982..304efdab 100644
--- a/libi2pd/SSU2Session.h
+++ b/libi2pd/SSU2Session.h
@@ -49,10 +49,10 @@ namespace transport
 	const float SSU2_kAPPA = 1.8;
 	const size_t SSU2_MAX_OUTGOING_QUEUE_SIZE = 500; // in messages
 	const int SSU2_MAX_NUM_ACNT = 255; // acnt, acks or nacks
-	const int SSU2_MAX_NUM_ACK_PACKETS = 510; // 2*255 ack + nack
+	const int SSU2_MAX_NUM_ACK_PACKETS = 511; // ackthrough + acnt + 1 range
 	const int SSU2_MAX_NUM_ACK_RANGES = 32; // to send
 	const uint8_t SSU2_MAX_NUM_FRAGMENTS = 64;
-	const int SSU2_SEND_DATETIME_NUM_PACKETS = 250;
+	const int SSU2_SEND_DATETIME_NUM_PACKETS = 256;
 
 	// flags
 	const uint8_t SSU2_FLAG_IMMEDIATE_ACK_REQUESTED = 0x01;