diff --git a/math/factorial/prolog/factorial.pl b/math/factorial/prolog/factorial.pl
index 82c09c860a..5a4a52ee00 100644
--- a/math/factorial/prolog/factorial.pl
+++ b/math/factorial/prolog/factorial.pl
@@ -34,6 +34,6 @@
 %recursion
 factorial(N, F) :- 
     N1 is N - 1,
-    fat(N1, N2),
+    factorial(N1, N2),
     F is N * N2.