diff --git a/src/libguac/user-handlers.c b/src/libguac/user-handlers.c
index 9cd558c1..4f1f59b0 100644
--- a/src/libguac/user-handlers.c
+++ b/src/libguac/user-handlers.c
@@ -95,30 +95,35 @@ int __guac_handle_sync(guac_user* user, int argc, char** argv) {
     if (timestamp > user->client->last_sent_timestamp)
         return -1;
 
-    /* Update stored timestamp */
-    user->last_received_timestamp = timestamp;
+    /* Only update lag calculations if timestamp is sane */
+    if (timestamp >= user->last_received_timestamp) {
 
-    /* Calculate length of frame, including network and processing lag */
-    frame_duration = current - timestamp;
+        /* Update stored timestamp */
+        user->last_received_timestamp = timestamp;
 
-    /* Update lag statistics if at least one frame has been rendered */
-    if (user->last_frame_duration != 0) {
+        /* Calculate length of frame, including network and processing lag */
+        frame_duration = current - timestamp;
 
-        /* Approximate processing lag by summing the frame duration deltas */
-        int processing_lag = user->processing_lag + frame_duration
-                           - user->last_frame_duration;
+        /* Update lag statistics if at least one frame has been rendered */
+        if (user->last_frame_duration != 0) {
 
-        /* Adjust back to zero if cumulative error leads to a negative value */
-        if (processing_lag < 0)
-            processing_lag = 0;
+            /* Calculate lag using the previous frame as a baseline */
+            int processing_lag = frame_duration - user->last_frame_duration;
 
-        user->processing_lag = processing_lag;
+            /* Adjust back to zero if cumulative error leads to a negative
+             * value */
+            if (processing_lag < 0)
+                processing_lag = 0;
+
+            user->processing_lag = processing_lag;
+
+        }
+
+        /* Record baseline duration of frame by excluding lag */
+        user->last_frame_duration = frame_duration - user->processing_lag;
 
     }
 
-    /* Record duration of frame */
-    user->last_frame_duration = frame_duration;
-
     if (user->sync_handler)
         return user->sync_handler(user, timestamp);
     return 0;
diff --git a/src/protocols/rdp/rdp.c b/src/protocols/rdp/rdp.c
index 893fde5e..389c7049 100644
--- a/src/protocols/rdp/rdp.c
+++ b/src/protocols/rdp/rdp.c
@@ -832,6 +832,13 @@ static int guac_rdp_handle_connection(guac_client* client) {
                     break;
 
             } while (wait_result > 0);
+
+            /* Record end of frame, excluding server-side rendering time (we
+             * assume server-side rendering time will be consistent between any
+             * two subsequent frames, and that this time should thus be
+             * excluded from the required wait period of the next frame). */
+            last_frame_end = frame_start;
+
         }
 
         /* If an error occurred, fail */
@@ -839,14 +846,11 @@ static int guac_rdp_handle_connection(guac_client* client) {
             guac_client_abort(client, GUAC_PROTOCOL_STATUS_UPSTREAM_ERROR,
                     "Connection closed.");
 
-        /* End of frame */
+        /* Flush frame */
         guac_common_display_flush(rdp_client->display);
         guac_client_end_frame(client);
         guac_socket_flush(client->socket);
 
-        /* Record end of frame */
-        last_frame_end = guac_timestamp_current();
-
     }
 
     pthread_mutex_lock(&(rdp_client->rdp_lock));
diff --git a/src/protocols/vnc/vnc.c b/src/protocols/vnc/vnc.c
index 992933d0..9b0bd769 100644
--- a/src/protocols/vnc/vnc.c
+++ b/src/protocols/vnc/vnc.c
@@ -380,6 +380,12 @@ void* guac_vnc_client_thread(void* data) {
 
             } while (wait_result > 0);
 
+            /* Record end of frame, excluding server-side rendering time (we
+             * assume server-side rendering time will be consistent between any
+             * two subsequent frames, and that this time should thus be
+             * excluded from the required wait period of the next frame). */
+            last_frame_end = frame_start;
+
         }
 
         /* If an error occurs, log it and fail */
@@ -391,9 +397,6 @@ void* guac_vnc_client_thread(void* data) {
         guac_client_end_frame(client);
         guac_socket_flush(client->socket);
 
-        /* Record end of frame */
-        last_frame_end = guac_timestamp_current();
-
     }
 
     /* Kill client and finish connection */