diff --git a/deprecate/deprecation.py b/deprecate/deprecation.py
index fc868f7..9be3d92 100644
--- a/deprecate/deprecation.py
+++ b/deprecate/deprecation.py
@@ -240,7 +240,8 @@ def packing(source: Callable) -> Callable:
         def wrapped_fn(*args: Any, **kwargs: Any) -> Any:
             # check if user requested a skip
             shall_skip = skip_if() if callable(skip_if) else bool(skip_if)
-            assert isinstance(shall_skip, bool), "function shall return bool"
+            if not isinstance(shall_skip, bool):
+                raise TypeError("User function `shall_skip` shall return bool, but got: %r" % type(shall_skip))
             if shall_skip:
                 return source(*args, **kwargs)
 
diff --git a/tests/collection_deprecate.py b/tests/collection_deprecate.py
index ba6b6d2..478a2df 100644
--- a/tests/collection_deprecate.py
+++ b/tests/collection_deprecate.py
@@ -116,3 +116,8 @@ def depr_pow_skip_if_true(base: float, c1: float = 1, nc1: float = 1) -> float:
 @deprecated(True, "0.1", "0.2", args_mapping=dict(c1='nc1'), template_mgs=_SHORT_MSG_ARGS, skip_if=lambda: True)
 def depr_pow_skip_if_func(base: float, c1: float = 1, nc1: float = 1) -> float:
     return base**(c1 - nc1)
+
+
+@deprecated(True, "0.1", "0.3", args_mapping=dict(c1='nc1'), template_mgs=_SHORT_MSG_ARGS, skip_if=lambda: 42)
+def depr_pow_skip_if_func_int(base: float, c1: float = 1, nc1: float = 1) -> float:
+    return base**(c1 - nc1)
diff --git a/tests/test_functions.py b/tests/test_functions.py
index cda45f2..797b69d 100644
--- a/tests/test_functions.py
+++ b/tests/test_functions.py
@@ -15,6 +15,7 @@
     depr_pow_self_twice,
     depr_pow_skip_if_false_true,
     depr_pow_skip_if_func,
+    depr_pow_skip_if_func_int,
     depr_pow_skip_if_true,
     depr_pow_skip_if_true_false,
     depr_pow_wrong,
@@ -150,6 +151,9 @@ def test_deprecated_func_skip_if() -> None:
     with pytest.deprecated_call(match='Depr: v0.1 rm v0.2 for args: `c1` -> `nc1`.'):
         assert depr_pow_skip_if_false_true(2, c1=2) == 0.5
 
+    with pytest.raises(TypeError, match="User function `shall_skip` shall return bool, but got: <class 'int'>"):
+        assert depr_pow_skip_if_func_int(2, c1=2)
+
 
 def test_deprecated_func_mapping() -> None:
     """Test mapping to external functions"""