diff --git a/.env.test b/.env.test
index ad24921..26254ec 100644
--- a/.env.test
+++ b/.env.test
@@ -11,3 +11,4 @@ RUNBOAT_BUILD_DOMAIN=runboat.odoo-community.org
 RUNBOAT_BUILD_ENV={}
 RUNBOAT_GITHUB_TOKEN=
 RUNBOAT_LOG_CONFIG=log-config.yaml
+RUNBOAT_BIULD_IMAGES={"15.0": "ghcr.io/oca/oca-ci/py3.8-odoo15.0:latest"}
diff --git a/README.md b/README.md
index e37912c..e3e1a62 100644
--- a/README.md
+++ b/README.md
@@ -152,7 +152,6 @@ More:
 - handle branch delete (delete all builds for branch)
 - create builds for all supported repos on startup (goes with sticky branches)
 - never undeploy last build of sticky branches
-- make build images configurable (see `build_images.py`)
 - configurable kubefiles directory
 - even more tests
 
diff --git a/src/runboat/build_images.py b/src/runboat/build_images.py
index f9f628f..54effca 100644
--- a/src/runboat/build_images.py
+++ b/src/runboat/build_images.py
@@ -1,21 +1,12 @@
 import re
 
 from .exceptions import BranchNotSupported
-
-images = {
-    "15.0": "ghcr.io/oca/oca-ci/py3.8-odoo15.0:latest",
-    "14.0": "ghcr.io/oca/oca-ci/py3.6-odoo14.0:latest",
-    "13.0": "ghcr.io/oca/oca-ci/py3.6-odoo13.0:latest",
-    "12.0": "ghcr.io/oca/oca-ci/py3.6-odoo12.0:latest",
-    "11.0": "ghcr.io/oca/oca-ci/py3.5-odoo11.0:latest",
-    "10.0": "ghcr.io/oca/oca-ci/py2.7-odoo10.0:latest",
-}
-
+from .settings import settings
 
 TARGET_BRANCH_RE = re.compile(r"^(\d+\.\d+)")
 
 
-def get_target_branch(branch_name: str) -> str:
+def get_main_branch(branch_name: str) -> str:
     mo = TARGET_BRANCH_RE.match(branch_name)
     if not mo:
         raise BranchNotSupported(
@@ -23,15 +14,26 @@ def get_target_branch(branch_name: str) -> str:
             f"(it should start with an Odoo branch name)."
         )
     key = mo.group(1)
-    if key not in images:
+    if key not in settings.build_images:
         raise BranchNotSupported(
             f"No build image configured for {key} (from {branch_name})."
         )
     return key
 
 
-check_branch_supported = get_target_branch
+def is_branch_supported(branch_name: str) -> bool:
+    try:
+        return bool(get_main_branch(branch_name))
+    except BranchNotSupported:
+        return False
+
+
+def is_main_branch(branch_name: str) -> bool:
+    try:
+        return branch_name == get_main_branch(branch_name)
+    except BranchNotSupported:
+        return False
 
 
 def get_build_image(branch_name: str) -> str:
-    return images[get_target_branch(branch_name)]
+    return settings.build_images[get_main_branch(branch_name)]
diff --git a/src/runboat/settings.py b/src/runboat/settings.py
index 0439a37..0b93f76 100644
--- a/src/runboat/settings.py
+++ b/src/runboat/settings.py
@@ -18,6 +18,14 @@ class Settings(BaseSettings):
     build_admin_passwd: str
     build_domain: str
     build_env: Optional[dict[str, str]]
+    build_images: dict[str, str] = {
+        "15.0": "ghcr.io/oca/oca-ci/py3.8-odoo15.0:latest",
+        "14.0": "ghcr.io/oca/oca-ci/py3.6-odoo14.0:latest",
+        "13.0": "ghcr.io/oca/oca-ci/py3.6-odoo13.0:latest",
+        "12.0": "ghcr.io/oca/oca-ci/py3.6-odoo12.0:latest",
+        "11.0": "ghcr.io/oca/oca-ci/py3.5-odoo11.0:latest",
+        "10.0": "ghcr.io/oca/oca-ci/py2.7-odoo10.0:latest",
+    }
     github_token: Optional[str]
     log_config: Optional[str]
 
diff --git a/tests/test_build_images.py b/tests/test_build_images.py
new file mode 100644
index 0000000..debf669
--- /dev/null
+++ b/tests/test_build_images.py
@@ -0,0 +1,24 @@
+import pytest
+
+from runboat.build_images import get_build_image, get_main_branch, is_branch_supported
+from runboat.exceptions import BranchNotSupported
+
+
+def test_get_main_branch():
+    assert get_main_branch("15.0") == "15.0"
+    assert get_main_branch("15.0-ocabot-merge") == "15.0"
+    with pytest.raises(BranchNotSupported):
+        get_main_branch("8.0")
+
+
+def test_is_branch_supported():
+    assert is_branch_supported("15.0")
+    assert is_branch_supported("15.0-ocabot-merge")
+    assert not is_branch_supported("8.0")
+
+
+def test_get_build_image():
+    assert get_build_image("15.0") == "ghcr.io/oca/oca-ci/py3.8-odoo15.0:latest"
+    assert get_build_image("15.0-zzz") == "ghcr.io/oca/oca-ci/py3.8-odoo15.0:latest"
+    with pytest.raises(BranchNotSupported):
+        get_build_image("8.0")