diff --git a/core/math/integers/integers.factor b/core/math/integers/integers.factor
index 27253b6da7..8c1ef6fa98 100644
--- a/core/math/integers/integers.factor
+++ b/core/math/integers/integers.factor
@@ -57,7 +57,9 @@ M: fixnum bitnot fixnum-bitnot ; inline
 M: fixnum bit? fixnum-bit? ; inline
 
 : fixnum-log2 ( x -- n )
-    0 swap [ dup 1 eq? ] [ [ 1 + ] [ 2/ ] bi* ] until drop ; inline
+    0 swap [ dup 1 eq? ] [
+        [ 1 fixnum+fast ] [ 2/ ] bi*
+    ] until drop ; inline
 
 M: fixnum (log2) fixnum-log2 ; inline