diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index c1d6f59ab2d36179290472ef80cf4abd061ca699..e685fbd7a1cc7541554ef83d91091bf57302fc7c 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -58,7 +58,7 @@ build:
   stage: build
   script:
     - *doc-workspace-do
-    - make
+    - make BUILD_DIR="$CI_PROJECT_DIR/build"
   artifacts:
     paths:
       - build
diff --git a/Makefile b/Makefile
index ec6ef548619623ca67d92e8d4a50f0d847dc2895..973359eaa0efdc127a354e88c5aedd4e80dd5a80 100644
--- a/Makefile
+++ b/Makefile
@@ -1,12 +1,16 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Huawei Inc.
 
+BUILD_DIR ?= build
+
 .PHONY: all
-all: build
+all: $(BUILD_DIR)
 
 .PHONY: clean
 clean:
 	rm -rf build
 
-build:
-	sphinx-build -W . build
+SRC_DIR ?= .
+# XXX: cannot add true dependencies because some file names contain spaces.
+$(BUILD_DIR):
+	sphinx-build -W $(SRC_DIR) $(BUILD_DIR)