diff --git a/config.mk b/config.mk
index 9bf4eda..05864aa 100644
--- a/config.mk
+++ b/config.mk
@@ -25,7 +25,7 @@
 # Check if arch/$ARCH/cpu/$CPU exists, otherwise assume arch/$ARCH/cpu contains
 # CPU-specific code.
 CPUDIR=arch/$(ARCH)/cpu/$(CPU)
-ifneq ($(SRCTREE)/$(CPUDIR),$(wildcard $(SRCTREE)/$(CPUDIR)))
+ifneq ($(srctree)/$(CPUDIR),$(wildcard $(srctree)/$(CPUDIR)))
 CPUDIR=arch/$(ARCH)/cpu
 endif