diff --git a/core/observe.c b/core/observe.c
index 6051f12..f5ee9a4 100644
--- a/core/observe.c
+++ b/core/observe.c
@@ -746,7 +746,7 @@ void observe_step(lwm2m_context_t * contextP,
                     {
                         LOG_ARG("Checking minimal period (%d s)", watcherP->parameters->minPeriod);
 
-                        if (watcherP->lastTime + watcherP->parameters->minPeriod > currentTime)
+                        if ((time_t)(watcherP->lastTime + watcherP->parameters->minPeriod) > currentTime)
                         {
                             // Minimum Period did not elapse yet
                             interval = watcherP->lastTime + watcherP->parameters->minPeriod - currentTime;
@@ -768,7 +768,7 @@ void observe_step(lwm2m_context_t * contextP,
                 {
                     LOG_ARG("Checking maximal period (%d s)", watcherP->parameters->maxPeriod);
 
-                    if (watcherP->lastTime + watcherP->parameters->maxPeriod <= currentTime)
+                    if ((time_t)(watcherP->lastTime + watcherP->parameters->maxPeriod) <= currentTime)
                     {
                         LOG("Notify on maximal period");
                         notify = true;