diff --git a/CMakeLists.txt b/CMakeLists.txt
index b377ea7..c976aaf 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -5,6 +5,8 @@ if(POLICY CMP0144)
 endif()
 include(FetchContent)
 
+set(C2PY_BRANCH "0.1.x")
+
 project(clair VERSION 0.1.0 LANGUAGES C CXX)
 get_directory_property(IS_SUBPROJECT PARENT_DIRECTORY)
 if (IS_SUBPROJECT)
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 2af03d0..b18a16d 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -5,7 +5,7 @@ set(IS_CLAIR_BUILD ON)
 FetchContent_Declare(
  c2py
  GIT_REPOSITORY  https://github.com/flatironinstitute/c2py
- GIT_TAG        unstable 
+ GIT_TAG        ${C2PY_BRANCH}
  EXCLUDE_FROM_ALL # we exclude from all so that c2py is NOT installed.
 )
 FetchContent_MakeAvailable(c2py)