diff --git a/drivers/arm/gic/v3/gicv3_private.h b/drivers/arm/gic/v3/gicv3_private.h
index 5e2409f..9aa8338 100644
--- a/drivers/arm/gic/v3/gicv3_private.h
+++ b/drivers/arm/gic/v3/gicv3_private.h
@@ -141,6 +141,7 @@
 
 static inline unsigned long long gicd_read_irouter(uintptr_t base, unsigned int id)
 {
+	assert(id >= MIN_SPI_ID);
 	return mmio_read_64(base + GICD_IROUTER + (id << 3));
 }
 
@@ -148,6 +149,7 @@
 				      unsigned int id,
 				      unsigned long long affinity)
 {
+	assert(id >= MIN_SPI_ID);
 	mmio_write_64(base + GICD_IROUTER + (id << 3), affinity);
 }
 
diff --git a/include/drivers/arm/gicv3.h b/include/drivers/arm/gicv3.h
index e915c07..b7ad778 100644
--- a/include/drivers/arm/gicv3.h
+++ b/include/drivers/arm/gicv3.h
@@ -55,7 +55,11 @@
 #define GICD_SETSPI_SR		0x50
 #define GICD_CLRSPI_SR		0x50
 #define GICD_IGRPMODR		0xd00
-#define GICD_IROUTER		0x6100
+/*
+ * GICD_IROUTER<n> register is at 0x6000 + 8n, where n is the interrupt id and
+ * n >= 32, making the effective offset as 0x6100.
+ */
+#define GICD_IROUTER		0x6000
 #define GICD_PIDR2_GICV3	0xffe8
 
 #define IGRPMODR_SHIFT		5