diff --git a/.github/workflows/develop.yml b/.github/workflows/develop.yml
index 63f09a6d..51b9454b 100644
--- a/.github/workflows/develop.yml
+++ b/.github/workflows/develop.yml
@@ -61,3 +61,10 @@ jobs:
           docker build -t otns-env -f etc/docker/environment/Dockerfile .
           docker run -t -v$PWD:/otns otns-env -c "./script/pack-web"
           git diff --quiet
+      - name: Build custom OT node
+        # Note: OT_CMAKE_NINJA_TARGET excludes tests because test_platform.cpp is missing otPlatAssertFail()
+        run: |
+          ./script/install-deps
+          ./script/setup-dev
+          cd ot-rfsim
+          OT_CMAKE_NINJA_TARGET="ot-cli-ftd ot-cli-mtd" ./script/build
diff --git a/ot-rfsim/script/build b/ot-rfsim/script/build
index c5f30be5..dfaaf119 100755
--- a/ot-rfsim/script/build
+++ b/ot-rfsim/script/build
@@ -29,8 +29,12 @@
 
 set -euxo pipefail
 
+# shellcheck source=../script/utils.sh
+. "$(dirname "$0")"/../../script/utils.sh
+
 OTRFSIM_SRCDIR="$(pwd)"
 OT_DIR=${OT_DIR:-../openthread}
+OT_DIR=$(realpathf "${OT_DIR}")
 OT_CMAKE_NINJA_TARGET=${OT_CMAKE_NINJA_TARGET-}
 readonly OTRFSIM_SRCDIR
 readonly OT_DIR
diff --git a/ot-rfsim/script/build_br b/ot-rfsim/script/build_br
index edae9453..3d978da1 100755
--- a/ot-rfsim/script/build_br
+++ b/ot-rfsim/script/build_br
@@ -61,7 +61,7 @@ main()
     local options=()
     options+=("${OTBR_OPTIONS[@]}" "$@")
 
-    OT_DIR="../openthread" OTNS_NODE_TYPE="br" OT_CMAKE_NINJA_TARGET="ot-cli-ftd" ./script/build "${options[@]}"
+    OTNS_NODE_TYPE="br" OT_CMAKE_NINJA_TARGET="ot-cli-ftd" ./script/build "${options[@]}"
 
     cp ./build/br/bin/ot-cli-ftd ./ot-versions/ot-cli-ftd_br
 }
diff --git a/ot-rfsim/script/build_latest b/ot-rfsim/script/build_latest
index 1592bf91..0e15040c 100755
--- a/ot-rfsim/script/build_latest
+++ b/ot-rfsim/script/build_latest
@@ -57,7 +57,7 @@ main()
     local options=()
     options+=("${OT_OPTIONS[@]}" "$@")
 
-    OT_DIR="../openthread" OTNS_NODE_TYPE="latest" OT_CMAKE_NINJA_TARGET="ot-cli-ftd ot-cli-mtd" ./script/build "${options[@]}"
+    OTNS_NODE_TYPE="latest" OT_CMAKE_NINJA_TARGET="ot-cli-ftd ot-cli-mtd" ./script/build "${options[@]}"
 
     cp ./build/latest/bin/ot-cli-ftd ./ot-versions/
     cp ./build/latest/bin/ot-cli-mtd ./ot-versions/
diff --git a/script/common.sh b/script/common.sh
index 34c92b70..8de8362e 100644
--- a/script/common.sh
+++ b/script/common.sh
@@ -43,9 +43,13 @@ fi
 SCRIPTDIR=$(realpathf "$(dirname "$0")")
 export readonly SCRIPTDIR
 
-OTNSDIR=$(realpathf "$SCRIPTDIR"/..)
+OTNSDIR=$(realpathf "${SCRIPTDIR}"/..)
 export readonly OTNSDIR
 
+OT_DIR=${OT_DIR:-./openthread}
+OT_DIR=$(realpathf "${OT_DIR}")
+export readonly OT_DIR
+
 GOPATH=$(go env GOPATH)
 export readonly GOPATH
 export PATH=$PATH:"$GOPATH"/bin
@@ -117,6 +121,7 @@ build_openthread_br()
     )
 }
 
+# Note: any environment var OT_DIR is not used for legacy node version (1.1, 1.2, 1.3) builds.
 build_openthread_versions()
 {
     get_openthread_versions
diff --git a/script/test b/script/test
index bd436855..6707ca4d 100755
--- a/script/test
+++ b/script/test
@@ -131,8 +131,8 @@ py_examples()
     install_deps
     activate_python_venv
     install_otns
-    build_openthread_br
     build_openthread
+    build_openthread_br
 
     check_py_example "$OTNSDIR"/pylibs/examples/simple.py
     check_py_example "$OTNSDIR"/pylibs/examples/form_partition.py
@@ -151,8 +151,8 @@ stress_tests()
     install_deps
     activate_python_venv
     install_otns
-    build_openthread_br
     build_openthread
+    build_openthread_br
 
     python3 "$OTNSDIR"/pylibs/stress_tests/run_stress_suite.py "$@"
 }