diff --git a/vac/raw/sds.md b/vac/raw/sds.md
index 0082a2d..2d909e5 100644
--- a/vac/raw/sds.md
+++ b/vac/raw/sds.md
@@ -81,7 +81,7 @@ message Message {
   string sender_id = 1;           // Participant ID of the message sender
   string message_id = 2;          // Unique identifier of the message
   string channel_id = 3;          // Identifier of the channel to which the message belongs
-  optional int32 lamport_timestamp = 10;    // Logical timestamp for causal ordering in channel
+  optional uint64 lamport_timestamp = 10;    // Logical timestamp for causal ordering in channel
   repeated HistoryEntry causal_history = 11;  // List of preceding message IDs that this message causally depends on. Generally 2 or 3 message IDs are included.
   optional bytes bloom_filter = 12;         // Bloom filter representing received message IDs in channel
   optional bytes content = 20;             // Actual content of the message
@@ -112,6 +112,10 @@ Each participant MUST maintain:
 
 * A Lamport timestamp for each channel of communication,
 initialized to current epoch time in millisecond resolution.
+The Lamport timestamp is increased as described in the [protocol steps](#protocol-steps)
+to maintain a logical ordering of events while staying close to the current epoch time.
+This allows the messages from new joiners to be correctly ordered with other recent messages,
+without these new participants first having to synchronize past messages to discover the current Lamport timestamp.
 * A bloom filter for received message IDs per channel.
 The bloom filter SHOULD be rolled over and
 recomputed once it reaches a predefined capacity of message IDs.
@@ -144,8 +148,11 @@ the `lamport_timestamp`, `causal_history` and `bloom_filter` fields.
 
 Before broadcasting a message:
 
-* the participant MUST increase its local Lamport timestamp by `1` and
-include this in the `lamport_timestamp` field.
+* the participant MUST set its local Lamport timestamp
+to the maximum between the current value + `1`
+and the current epoch time in milliseconds.
+In other words the local Lamport timestamp is set to `max(timeNowInMs, current_lamport_timestamp + 1)`.
+* the participant MUST include the increased Lamport timestamp in the message's `lamport_timestamp` field.
 * the participant MUST determine the preceding few message IDs in the local history
 and include these in an ordered list in the `causal_history` field.
 The number of message IDs to include in the `causal_history` depends on the application.
@@ -250,7 +257,8 @@ participants SHOULD periodically send sync messages to maintain state.
 These sync messages:
 
 * MUST be sent with empty content
-* MUST include an incremented Lamport timestamp
+* MUST include a Lamport timestamp increased to `max(timeNowInMs, current_lamport_timestamp + 1)`,
+where `timeNowInMs` is the current epoch time in milliseconds.
 * MUST include causal history and bloom filter according to regular message rules
 * MUST NOT be added to the unacknowledged outgoing buffer
 * MUST NOT be included in causal histories of subsequent messages