diff --git a/src/soc/intel/common/block/fast_spi/fast_spi.c b/src/soc/intel/common/block/fast_spi/fast_spi.c
index e46effc..78225ec 100644
--- a/src/soc/intel/common/block/fast_spi/fast_spi.c
+++ b/src/soc/intel/common/block/fast_spi/fast_spi.c
@@ -530,6 +530,11 @@
 
 	/* Add SPI flash MMIO window as a reserved resource. */
 	mmio_resource_kb(dev, 0, FLASH_BASE_ADDR / KiB, FLASH_MMIO_SIZE / KiB);
+	/* Add extended SPI flash MMIO window as reserved resource if enabled. */
+	if (CONFIG(FAST_SPI_SUPPORTS_EXT_BIOS_WINDOW)) {
+		mmio_resource_kb(dev, 1, CONFIG_EXT_BIOS_WIN_BASE / KiB,
+				 CONFIG_EXT_BIOS_WIN_SIZE / KiB);
+	}
 }
 
 static struct device_operations fast_spi_dev_ops = {