diff --git a/lib/resctrl_alloc.c b/lib/resctrl_alloc.c
index 1432ef78..d1c966e4 100644
--- a/lib/resctrl_alloc.c
+++ b/lib/resctrl_alloc.c
@@ -756,10 +756,8 @@ resctrl_alloc_task_validate(const pid_t task)
 
 	memset(buf, 0, sizeof(buf));
 	snprintf(buf, sizeof(buf)-1, "/proc/%d", (int)task);
-	if (access(buf, F_OK) != 0) {
-		LOG_ERROR("Task %d does not exist!\n", (int)task);
+	if (access(buf, F_OK) != 0)
 		return PQOS_RETVAL_ERROR;
-	}
 
 	return PQOS_RETVAL_OK;
 }
@@ -772,8 +770,10 @@ resctrl_alloc_task_write(const unsigned class_id, const pid_t task)
 
 	/* Check if task exists */
 	ret = resctrl_alloc_task_validate(task);
-	if (ret != PQOS_RETVAL_OK)
+	if (ret != PQOS_RETVAL_OK) {
+		LOG_ERROR("Task %d does not exist!\n", (int)task);
 		return PQOS_RETVAL_PARAM;
+	}
 
 	/* Open resctrl tasks file */
 	fd = resctrl_alloc_fopen(class_id, rctl_tasks, "w");
@@ -867,8 +867,10 @@ resctrl_alloc_task_search(unsigned *class_id,
 
 	/* Check if task exists */
 	ret = resctrl_alloc_task_validate(task);
-	if (ret != PQOS_RETVAL_OK)
+	if (ret != PQOS_RETVAL_OK) {
+		LOG_ERROR("Task %d does not exist!\n", (int)task);
 		return PQOS_RETVAL_PARAM;
+	}
 
 	/* Get number of COS */
 	ret = resctrl_alloc_get_grps_num(cap, &max_cos);
diff --git a/lib/resctrl_monitoring.c b/lib/resctrl_monitoring.c
index c128f910..4e1c3c0b 100644
--- a/lib/resctrl_monitoring.c
+++ b/lib/resctrl_monitoring.c
@@ -910,6 +910,12 @@ resctrl_mon_stop(struct pqos_mon_data *group)
                 for (i = 0; i < group->tid_nr; i++) {
                         const pid_t tid = group->tid_map[i];
 
+                        if (resctrl_alloc_task_validate(tid) !=
+                            PQOS_RETVAL_OK) {
+                                LOG_DEBUG("resctrl_mon_stop: Skipping "
+                                          "non-existant PID: %d\n", tid);
+                                continue;
+                        }
                         ret = resctrl_mon_assoc_set_pid(tid, NULL);
                         if (ret != PQOS_RETVAL_OK)
                                 goto resctrl_mon_stop_exit;