diff --git a/os/rt/src/chvt.c b/os/rt/src/chvt.c
index 1baa31e5d..d28b3d939 100644
--- a/os/rt/src/chvt.c
+++ b/os/rt/src/chvt.c
@@ -612,7 +612,7 @@ void chVTDoTickI(void) {
   }
 #else /* CH_CFG_ST_TIMEDELTA > 0 */
   virtual_timer_t *vtp;
-  sysinterval_t delta, nowdelta;
+  sysinterval_t nowdelta;
   systime_t now;
 
   /* Looping through timers consuming all timers with deltas lower or equal
@@ -663,11 +663,13 @@ void chVTDoTickI(void) {
     return;
   }
 
-  /* Calculating the delta to the next alarm time.*/
-  delta = vtp->dlist.delta - nowdelta;
+  /* The "unprocessed nowdelta" time slice is added to "last time"
+     and subtracted to next timer's delta.*/
+  vtlp->lasttime += nowdelta;
+  vtp->dlist.delta -= nowdelta;
 
   /* Update alarm time to next timer.*/
-  vt_set_alarm(now, delta);
+  vt_set_alarm(now, vtp->dlist.delta);
 #endif /* CH_CFG_ST_TIMEDELTA > 0 */
 }
 
diff --git a/readme.txt b/readme.txt
index 7061e3363..448dce4d1 100644
--- a/readme.txt
+++ b/readme.txt
@@ -75,6 +75,7 @@
 
 *** 20.3.5 ***
 - FIX: Some MISRA-related fixes.
+- FIX: Fixed Virtual Timers failure in a specific condition (bug #1215).
 - FIX: Fixed invalid state transition in SNOR flash driver (bug #1212).
 - FIX: Fixed missing check in chobjcaches.h (bug #1210).
 - FIX: Fixed RT testbuild application broken (bug #1208).