diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
index e80fe0ca24..4bb11960ee 100644
--- a/xen/arch/arm/gic.c
+++ b/xen/arch/arm/gic.c
@@ -111,7 +111,8 @@ static void gic_set_irq_priority(struct irq_desc *desc, unsigned int priority)
 void gic_route_irq_to_xen(struct irq_desc *desc, unsigned int priority)
 {
     ASSERT(priority <= 0xff);     /* Only 8 bits of priority */
-    ASSERT(desc->irq < gic_number_lines());/* Can't route interrupts that don't exist */
+    /* Can't route interrupts that don't exist */
+    ASSERT(gic_is_valid_line(desc->irq));
     ASSERT(test_bit(_IRQ_DISABLED, &desc->status));
     ASSERT(spin_is_locked(&desc->lock));
 
diff --git a/xen/arch/arm/include/asm/gic.h b/xen/arch/arm/include/asm/gic.h
index 541f0eeb80..3fcee42675 100644
--- a/xen/arch/arm/include/asm/gic.h
+++ b/xen/arch/arm/include/asm/gic.h
@@ -306,6 +306,15 @@ extern void gic_dump_vgic_info(struct vcpu *v);
 
 /* Number of interrupt lines */
 extern unsigned int gic_number_lines(void);
+static inline bool gic_is_valid_line(unsigned int irq)
+{
+    return irq < gic_number_lines();
+}
+
+static inline bool gic_is_spi(unsigned int irq)
+{
+    return irq >= NR_LOCAL_IRQS && gic_is_valid_line(irq);
+}
 
 /* IRQ translation function for the device tree */
 int gic_irq_xlate(const u32 *intspec, unsigned int intsize,
diff --git a/xen/arch/arm/irq.c b/xen/arch/arm/irq.c
index 02ca82c089..29524e5d53 100644
--- a/xen/arch/arm/irq.c
+++ b/xen/arch/arm/irq.c
@@ -418,7 +418,7 @@ err:
 bool is_assignable_irq(unsigned int irq)
 {
     /* For now, we can only route SPIs to the guest */
-    return (irq >= NR_LOCAL_IRQS) && (irq < gic_number_lines());
+    return gic_is_spi(irq);
 }
 
 /*