diff --git a/CMakeLists.txt b/CMakeLists.txt
index 717849017..d6fa4bd85 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -16,7 +16,9 @@ find_package(
 
 python_add_library(cutils
                    MODULE
-                   src/asammdf/blocks/cutils.c)
+                   src/asammdf/blocks/cutils.c
+                   WITH_SOABI USE_SABI 3.9)
+
 target_link_libraries(cutils PRIVATE Python::NumPy)
 
 install(TARGETS cutils DESTINATION "asammdf/blocks")
diff --git a/pyproject.toml b/pyproject.toml
index a5c5fa990..c6b9c0a14 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -78,6 +78,7 @@ Source = "https://github.com/danielhrisca/asammdf"
 metadata.version.provider = "scikit_build_core.metadata.regex"
 metadata.version.input = "src/asammdf/version.py"
 wheel.packages = ["src/asammdf"]
+wheel.py-api = "cp39"
 
 [tool.black]
 line-length = 120
diff --git a/src/asammdf/blocks/cutils.c b/src/asammdf/blocks/cutils.c
index 5f2e6ac25..13f1e03e1 100644
--- a/src/asammdf/blocks/cutils.c
+++ b/src/asammdf/blocks/cutils.c
@@ -1529,7 +1529,7 @@ static PyObject *bytes_dtype_size(PyObject *self, PyObject *args)
                 break;
             }
             
-            current_size = PyBytes_GET_SIZE(*pointer);
+            current_size = PyBytes_Size(*pointer);
             
             if (current_size > size) size = current_size;
         }