diff --git a/Makefile b/Makefile
index 9a2cf40..d6f537f 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,3 @@
-OUT ?= out
-
 # Set path to prebuilts used in the build.
 UNNAME_S := $(shell uname -s | tr '[:upper:]' '[:lower:]')
 PREBUILTS := $(PWD)/prebuilts/$(UNNAME_S)-x64
@@ -8,22 +6,27 @@
 export PATH := $(PREBUILTS)/clang/bin:$(PATH)
 
 # Configure the build arguments.
-GCC ?= false
 ARCH ?= aarch64
 PLATFORM ?= qemu
+GCC ?= false
+
+# Place builds for different architectures and platforms in different
+# directories.
+OUT ?= out
+OUT_DIR = out/$(ARCH)/$(PLATFORM)
 
 .PHONY: all
-all: $(OUT)/build.ninja
-	@$(NINJA) -C $(OUT)
+all: $(OUT_DIR)/build.ninja
+	@$(NINJA) -C $(OUT_DIR)
 
-$(OUT)/build.ninja: $(OUT)/args.gn
-	@$(GN) --export-compile-commands gen $(OUT)
+$(OUT_DIR)/build.ninja: $(OUT_DIR)/args.gn
+	@$(GN) --export-compile-commands gen $(OUT_DIR)
 
 # Configure the build by loading the configuration arguments for the
 # architecture and platform.
-$(OUT)/args.gn: build/arch/$(ARCH)/$(PLATFORM).args
+$(OUT_DIR)/args.gn: build/arch/$(ARCH)/$(PLATFORM).args
 	@echo Copying config for $(ARCH) on $(PLATFORM)
-	@mkdir -p $(OUT)
+	@mkdir -p $(OUT_DIR)
 	@echo "arch = \"$(ARCH)\"" >> $@
 	@echo "use_gcc = $(GCC)" >> $@
 	@echo >> $@
@@ -31,8 +34,8 @@
 
 .PHONY: clean
 clean:
-	@$(NINJA) -C $(OUT) -t clean
-	rm -f $(OUT)/args.gn
+	@$(NINJA) -C $(OUT_DIR) -t clean
+	rm -f $(OUT_DIR)/args.gn
 
 .PHONY: clobber
 clobber:
@@ -49,15 +52,15 @@
 
 # see .clang-tidy.
 .PHONY: tidy
-tidy: $(OUT)/build.ninja
-	@$(NINJA) -C $(OUT)
+tidy: $(OUT_DIR)/build.ninja
+	@$(NINJA) -C $(OUT_DIR)
 	@echo "Tidying..."
-	@find src/ -name *.c -exec clang-tidy -p $(OUT) -fix {} \;
-	@find test/ -name *.c -exec clang-tidy -p $(OUT) -fix {} \;
+	@find src/ -name *.c -exec clang-tidy -p $(OUT_DIR) -fix {} \;
+	@find test/ -name *.c -exec clang-tidy -p $(OUT_DIR) -fix {} \;
 
 .PHONY: check
-check: $(OUT)/build.ninja
-	@$(NINJA) -C $(OUT)
+check: $(OUT_DIR)/build.ninja
+	@$(NINJA) -C $(OUT_DIR)
 	@echo "Checking..."
-	@find src/ -name *.c -exec clang-check -p $(OUT) -analyze {} \;
-	@find test/ -name *.c -exec clang-check -p $(OUT) -analyze {} \;
+	@find src/ -name *.c -exec clang-check -p $(OUT_DIR) -analyze {} \;
+	@find test/ -name *.c -exec clang-check -p $(OUT_DIR) -analyze {} \;
diff --git a/kokoro/ubuntu/build.sh b/kokoro/ubuntu/build.sh
index 4596757..9a7f510 100755
--- a/kokoro/ubuntu/build.sh
+++ b/kokoro/ubuntu/build.sh
@@ -11,17 +11,18 @@
 then
 	# Server
 	cd git/hafnium
-	make out/args.gn
 else
 	# Local
 	echo "Testing kokoro build locally..."
-	make out/args.gn
 fi
 
 #
 # Step 1: make sure it builds.
 #
 
+export ARCH=aarch64
+export PLATFORM=qemu
+
 # TODO: add a gcc-4.9 or above prebuilt to check the gcc build too?
 # Check the build works.
 make
diff --git a/kokoro/ubuntu/test.sh b/kokoro/ubuntu/test.sh
index c313d6d..623c4aa 100755
--- a/kokoro/ubuntu/test.sh
+++ b/kokoro/ubuntu/test.sh
@@ -10,8 +10,8 @@
 
 TIMEOUT="timeout --foreground"
 QEMU="./prebuilts/linux-x64/qemu/qemu-system-aarch64 -M virt -cpu cortex-a57 -m 8M -machine virtualization=true -nographic -nodefaults -serial stdio"
-HAFNIUM="out/clang_aarch64/hafnium.bin"
-INITRD="out/clang_aarch64/initrd"
+HAFNIUM="out/aarch64/qemu/clang_aarch64/hafnium.bin"
+INITRD="out/aarch64/qemu/clang_aarch64/initrd"
 
 # Run the QEMU tests with a timeout so they can't loop forever.
 $TIMEOUT 5s $QEMU -kernel $HAFNIUM -initrd $INITRD/primary_only_test.img