diff --git a/defaults-o2-acts.sh b/defaults-o2-acts.sh
new file mode 100644
index 0000000000..a5dd3994e6
--- /dev/null
+++ b/defaults-o2-acts.sh
@@ -0,0 +1,65 @@
+package: defaults-o2-acts
+version: v1
+env:
+  CFLAGS: -fPIC -O2
+  CMAKE_BUILD_TYPE: RELWITHDEBINFO
+  CXXFLAGS: -fPIC -O2 -std=c++20
+  CXXSTD: '20'
+  ENABLE_VMC: 'ON'
+  GEANT4_BUILD_MULTITHREADED: 'OFF'
+  MACOSX_DEPLOYMENT_TARGET: '14.0'
+disable:
+  - mesos
+  - MySQL
+overrides:
+  cgal:
+    version: 4.12.2
+  O2:
+    requires:
+        - abseil
+        - arrow
+        - FairRoot
+        - Vc
+        - HepMC3
+        - libInfoLogger
+        - Common-O2
+        - Configuration
+        - Monitoring
+        - ms_gsl
+        - FairMQ
+        - curl
+        - MCStepLogger
+        - fmt
+        - "openmp:(?!osx.*)"
+        - DebugGUI
+        - JAliEn-ROOT
+        - fastjet
+        - libuv
+        - libjalienO2
+        - cgal
+        - "VecGeom:(?!osx.*)"
+        - FFTW3
+        - ONNXRuntime
+        - nlohmann_json
+        - MLModels
+        - RapidJSON
+        - bookkeeping-api
+        - AliEn-CAs
+        - gpu-system
+        - Eigen3
+        - GBL
+        - ACTS
+    build_requires:
+        - abseil
+        - GMP
+        - MPFR
+        - googlebenchmark
+        - O2-customization
+        - Clang:(?!osx*)
+---
+# This file is included in any build recipe and it's only used to set
+# environment variables. Which file to actually include can be defined by the
+# "--defaults" option of alibuild.
+# 
+# This defaults file enables ACTS for building ACTSO2.
+# Usage: aliBuild build ACTSO2 --defaults o2-acts
diff --git a/o2-customization.sh b/o2-customization.sh
index 8b497aa795..03a1c193b8 100644
--- a/o2-customization.sh
+++ b/o2-customization.sh
@@ -5,6 +5,7 @@ env:
 valid_defaults:
   - o2
   - o2-dataflow
+  - o2-acts
   - o2-epn
   - o2-dev-fairroot
   - alo
diff --git a/o2.sh b/o2.sh
index c6b62517bb..798a2c02af 100644
--- a/o2.sh
+++ b/o2.sh
@@ -161,6 +161,7 @@ incremental_recipe: |
 
 valid_defaults:
   - o2
+  - o2-acts
   - o2-dataflow
   - o2-epn
   - o2-dev-fairroot