diff --git a/src/mainboard/system76/cml-u/Kconfig b/src/mainboard/system76/cml-u/Kconfig
index 8ba153e6a6..161252caa0 100644
--- a/src/mainboard/system76/cml-u/Kconfig
+++ b/src/mainboard/system76/cml-u/Kconfig
@@ -17,6 +17,7 @@ config BOARD_SPECIFIC_OPTIONS
 	select MAINBOARD_HAS_TPM2
 	select NO_UART_ON_SUPERIO
 	select PCIEXP_HOTPLUG
+	select PCIEXP_HOTPLUG_PREFETCH_MEM_BELOW_4G # Fix running out of MTRRs
 	select SOC_INTEL_COMETLAKE
 	select SOC_INTEL_COMMON_ACPI_EC_PTS_WAK
 	select SOC_INTEL_COMMON_BLOCK_HDA
diff --git a/src/mainboard/system76/whl-u/Kconfig b/src/mainboard/system76/whl-u/Kconfig
index ffe8624c60..3affacee69 100644
--- a/src/mainboard/system76/whl-u/Kconfig
+++ b/src/mainboard/system76/whl-u/Kconfig
@@ -17,6 +17,7 @@ config BOARD_SPECIFIC_OPTIONS
 	select MAINBOARD_HAS_TPM2
 	select NO_UART_ON_SUPERIO
 	select PCIEXP_HOTPLUG
+	select PCIEXP_HOTPLUG_PREFETCH_MEM_BELOW_4G # Fix running out of MTRRs
 	select SOC_INTEL_COMMON_ACPI_EC_PTS_WAK
 	select SOC_INTEL_COMMON_BLOCK_HDA
 	select SOC_INTEL_COMMON_BLOCK_HDA_VERB