diff --git a/concrete/numpy/internal/__init__.py b/concrete/numpy/internal/__init__.py
new file mode 100644
index 000000000..065af833e
--- /dev/null
+++ b/concrete/numpy/internal/__init__.py
@@ -0,0 +1,3 @@
+"""
+Declaration of `concrete.numpy.internal` namespace.
+"""
diff --git a/concrete/numpy/internal/utils.py b/concrete/numpy/internal/utils.py
new file mode 100644
index 000000000..804f4fe6c
--- /dev/null
+++ b/concrete/numpy/internal/utils.py
@@ -0,0 +1,31 @@
+"""
+Declaration of various functions and constants related to the entire project.
+"""
+
+
+def assert_that(condition: bool, message: str = ""):
+    """
+    Assert a condition.
+
+    Args:
+        condition (bool):
+            condition to assert
+
+        message (str):
+            message to give to `AssertionError` if the condition does not hold
+
+    Raises:
+        AssertionError:
+            if the condition does not hold
+    """
+
+    if not condition:
+        raise AssertionError(message)
+
+
+def unreachable():
+    """
+    Raise a RuntimeError to indicate unreachable code is entered.
+    """
+
+    raise RuntimeError("Entered unreachable code")