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 e46effcc4e..78225ec0d8 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 @@ static void fast_spi_read_resources(struct device *dev)
 
 	/* 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 = {
diff --git a/src/soc/intel/common/block/systemagent/systemagent.c b/src/soc/intel/common/block/systemagent/systemagent.c
index 1ceddf34d6..0861e62fc8 100644
--- a/src/soc/intel/common/block/systemagent/systemagent.c
+++ b/src/soc/intel/common/block/systemagent/systemagent.c
@@ -289,11 +289,6 @@ static void systemagent_read_resources(struct device *dev)
 	if (CONFIG(SA_ENABLE_IMR))
 		/* Add the isolated memory ranges (IMRs). */
 		sa_add_imr_resources(dev, &index);
-
-	/* Reserve the window used for extended BIOS decoding. */
-	if (CONFIG(FAST_SPI_SUPPORTS_EXT_BIOS_WINDOW))
-		mmio_resource_kb(dev, index++, CONFIG_EXT_BIOS_WIN_BASE / KiB,
-			      CONFIG_EXT_BIOS_WIN_SIZE / KiB);
 }
 
 void enable_power_aware_intr(void)