diff --git a/sched/irq/irq_attach.c b/sched/irq/irq_attach.c
index a992c927931..690d059ad99 100644
--- a/sched/irq/irq_attach.c
+++ b/sched/irq/irq_attach.c
@@ -111,7 +111,7 @@ int irq_attach(int irq, xcpt_t isr, FAR void *arg)
 #if NR_IRQS > 0
   int ret = -EINVAL;
 
-  if ((unsigned)irq < NR_IRQS)
+  if (irq >= 0 && irq < NR_IRQS)
     {
       int ndx = IRQ_TO_NDX(irq);
       irqstate_t flags;
diff --git a/sched/irq/irq_attach_thread.c b/sched/irq/irq_attach_thread.c
index ef5f98e599c..02d47b58505 100644
--- a/sched/irq/irq_attach_thread.c
+++ b/sched/irq/irq_attach_thread.c
@@ -99,7 +99,7 @@ static int isr_thread_main(int argc, FAR char *argv[])
   info.arg = arg;
   info.handler = isr;
 
-  nxsem_init(&sem, 0, 0);
+  nxsem_init(&sem, 0, 0u);
 
   irq_attach(irq, irq_thread_default_handler, &info);
 
@@ -159,7 +159,7 @@ int irq_attach_thread(int irq, xcpt_t isr, xcpt_t isrthread, FAR void *arg,
   pid_t pid;
   int ndx;
 
-  if ((unsigned)irq >= NR_IRQS)
+  if (irq < 0 || irq >= NR_IRQS)
     {
       return -EINVAL;
     }
diff --git a/sched/irq/irq_attach_wqueue.c b/sched/irq/irq_attach_wqueue.c
index fc1eb11539d..7f7b33ed9b4 100644
--- a/sched/irq/irq_attach_wqueue.c
+++ b/sched/irq/irq_attach_wqueue.c
@@ -138,7 +138,7 @@ static int irq_default_handler(int irq, FAR void *regs, FAR void *arg)
 
   if (ret == IRQ_WAKE_THREAD)
     {
-      work_queue_wq(info->wqueue, &info->work, irq_work_handler, info, 0);
+      work_queue_wq(info->wqueue, &info->work, irq_work_handler, info, 0u);
       ret = OK;
     }
 
@@ -179,7 +179,7 @@ int irq_attach_wqueue(int irq, xcpt_t isr, xcpt_t isrwork,
 #if NR_IRQS > 0
   int ndx;
 
-  if ((unsigned)irq >= NR_IRQS)
+  if (irq < 0 || irq >= NR_IRQS)
     {
       return -EINVAL;
     }
diff --git a/sched/irq/irq_dispatch.c b/sched/irq/irq_dispatch.c
index 71dc5a14762..0b8cde958d6 100644
--- a/sched/irq/irq_dispatch.c
+++ b/sched/irq/irq_dispatch.c
@@ -102,10 +102,10 @@ void irq_dispatch(int irq, FAR void *context)
 #endif
   xcpt_t vector = irq_unexpected_isr;
   FAR void *arg = NULL;
-  unsigned int ndx = irq;
+  int ndx = irq;
 
 #if NR_IRQS > 0
-  if ((unsigned)irq < NR_IRQS)
+  if (irq >= 0 && irq < NR_IRQS)
     {
 #ifdef CONFIG_ARCH_MINIMAL_VECTORTABLE
       ndx = g_irqmap[irq];