diff --git a/pybayes/pdfs.py b/pybayes/pdfs.py
index c752911..3935c4e 100644
--- a/pybayes/pdfs.py
+++ b/pybayes/pdfs.py
@@ -42,8 +42,8 @@ def __init__(self, dimension, name = None):
         if name is not None and not isinstance(name, str):
             raise TypeError("name must be either None or a string")
         self.name = name
-        if not isinstance(dimension, int):
-            raise TypeError("dimension must be integer (int)")
+        if not isinstance(dimension, long):
+            raise TypeError("dimension must be integer (long)")
         if dimension < 1:
             raise ValueError("dimension must be non-zero positive")
         self.dimension = dimension