diff --git a/arch/misoc/include/irq.h b/arch/misoc/include/irq.h
index 1fbf884fc3b..a21987b00a4 100644
--- a/arch/misoc/include/irq.h
+++ b/arch/misoc/include/irq.h
@@ -53,7 +53,11 @@
  * Pre-processor Definitions
  ****************************************************************************/
 
-#define NR_IRQS 32
+/* 32 True interrupts plus the sofware interrupt */
+
+#define MISOC_NINTERRUPTS 32
+#define MISOC_IRQ_SWINT   32
+#define NR_IRQS           33
 
 /****************************************************************************
  * Public Function Prototypes
diff --git a/arch/misoc/src/lm32/lm32_decodeirq.c b/arch/misoc/src/lm32/lm32_decodeirq.c
index bdf0abe240d..0df3f73ed96 100644
--- a/arch/misoc/src/lm32/lm32_decodeirq.c
+++ b/arch/misoc/src/lm32/lm32_decodeirq.c
@@ -77,7 +77,7 @@ uint32_t *lm32_decodeirq(uint32_t *regs)
 
   /* Decode and dispatch interrupts */
 
-  for (irq = 0; irq < NR_IRQS & instat != 0; i++)
+  for (irq = 0; irq < MISOC_NINTERRUPTS & instat != 0; i++)
     {
       uint32_t bit = (1 << irq);
 
diff --git a/arch/misoc/src/lm32/lm32_irq.c b/arch/misoc/src/lm32/lm32_irq.c
index d64623dfa3e..4218d8872b2 100644
--- a/arch/misoc/src/lm32/lm32_irq.c
+++ b/arch/misoc/src/lm32/lm32_irq.c
@@ -74,6 +74,13 @@ void lm32_irq_initialize(void)
   irq_setie(1);
 }
 
+/****************************************************************************
+ * Name: up_irq_save
+ *
+ * Description:
+ *
+ ****************************************************************************/
+
 irqstate_t up_irq_save(void)
 {
   irqstate_t flags;
@@ -88,6 +95,13 @@ irqstate_t up_irq_save(void)
   return flags;
 }
 
+/****************************************************************************
+ * Name: up_irq_restore
+ *
+ * Description:
+ *
+ ****************************************************************************/
+
 void up_irq_restore(irqstate_t flags)
 {
   /* Restore the interrupt state returned by up_save_irq() */
@@ -109,11 +123,16 @@ void up_disable_irq(int irq)
 
   DEBUGASSERT(irq >= 0 && irq < NR_IRQS);
 
-  /* Disable interrupts by clearing the bit that corresponds to the irq */
+  /* Ignore any attempt to disable software interrupts */
 
-  flags  = irq_getmask();
-  flags &= ~(1 << irq);
-  irq_setmask(flags);
+  if (irq < MISOC_NINTERRUPTS)
+    {
+      /* Disable interrupts by clearing the bit that corresponds to the irq */
+
+      flags  = irq_getmask();
+      flags &= ~(1 << irq);
+      irq_setmask(flags);
+    }
 }
 
 /****************************************************************************
@@ -129,9 +148,14 @@ void up_enable_irq(int irq)
   irqstate_t flags;
   DEBUGASSERT(irq >= 0 && irq < NR_IRQS);
 
-  /* Enable interrupts by setting the bit that corresponds to the irq */
+  /* Ignore any attempt to enable software interrupts */
 
-  flags  = irq_getmask();
-  flags |= (1 << irq);
-  irq_setmask(flags);
+  if (irq < MISOC_NINTERRUPTS)
+    {
+      /* Enable interrupts by setting the bit that corresponds to the irq */
+
+      flags  = irq_getmask();
+      flags |= (1 << irq);
+      irq_setmask(flags);
+    }
 }