diff --git a/src/cell.c b/src/cell.c
index 094645ba50e35cd06e3a3f0c333741cb34d4858d..dfbfe5fc003ee6a6a55bb3ac5a57642841e388c6 100644
--- a/src/cell.c
+++ b/src/cell.c
@@ -829,12 +829,10 @@ int cell_is_drift_needed(struct cell *c, int ti_current) {
     if (l->t->type != task_type_pair && l->t->type != task_type_sub_pair)
       continue;
 
-    /* Left or right? */
-    if (l->t->ci == c) {
-      if (l->t->cj->ti_end_min == ti_current) return 1;
-    } else if (l->t->cj == c) {
-      if (l->t->ci->ti_end_min == ti_current) return 1;
-    }
+    /* Does the other cell in the pair have an active particle ? */
+    if ((l->t->ci == c) && (l->t->cj->ti_end_min == ti_current) ||
+        (l->t->cj == c) && (l->t->ci->ti_end_min == ti_current))
+      return 1;
   }
 
   /* No neighbouring cell has active particles. Drift not necessary */
diff --git a/src/runner.c b/src/runner.c
index 57a6b9de7017ccb953eaaf05d9880cc440bdd974..87de99ba7255b89495149566069bcc0cb3c638b4 100644
--- a/src/runner.c
+++ b/src/runner.c
@@ -650,6 +650,9 @@ static void runner_do_drift(struct cell *c, struct engine *e) {
   /* Do we need to drift ? */
   if (!e->drift_all && !cell_is_drift_needed(c, ti_current)) return;
 
+  /* Check that we are actually going to move forward. */
+  if (ti_current == ti_old) return;
+
   /* Drift from the last time the cell was drifted to the current time */
   const double dt = (ti_current - ti_old) * timeBase;