diff --git a/src/timer.h b/src/timer.h
index c441420..4d45538 100644
--- a/src/timer.h
+++ b/src/timer.h
@@ -92,7 +92,13 @@ class Timer {
             struct task * const task = &tasks[i];
             const unsigned long duration = t - task->start;
 
-            if (task->handler && duration >= task->expires) {
+            // Tasks that were generated by a task earlier in the loop could have
+            // a start time larger than the "current time" given as an argument.
+            //
+            // Check if t >= task->start to prevent the underflow from triggering tasks early.
+            // 
+            // See https://github.com/contrem/arduino-timer/pull/7 for more info.
+            if (task->handler && t >= task->start && duration >= task->expires) {
                 task->repeat = task->handler(task->opaque) && task->repeat;
 
                 if (task->repeat) task->start = t;