diff --git a/src/misc/timer.cpp b/src/misc/timer.cpp
index e3239eb7..49900513 100644
--- a/src/misc/timer.cpp
+++ b/src/misc/timer.cpp
@@ -127,6 +127,12 @@ void Timer::run()
             work->processing = false;
 
             if(work->period > 0.0 && alive && !work->cancelled) {
+                if(waitfor <= -work->period) {
+                    // Periodic timer phase has fallen behind by at least one full period.
+                    // Could be due to previous slow jobs, or a system time jump forward.
+                    // Reset the phase.
+                    work->timeToRun = now = epicsTime::getCurrent();
+                }
                 work->timeToRun += work->period;
                 addElement(work);
             }