diff --git a/extra/math/miller-rabin/miller-rabin.factor b/extra/math/miller-rabin/miller-rabin.factor
index cd20216ff9..661d0fb29a 100644
--- a/extra/math/miller-rabin/miller-rabin.factor
+++ b/extra/math/miller-rabin/miller-rabin.factor
@@ -18,9 +18,7 @@ SYMBOL: trials
 : next-odd ( m -- n )
     dup even? [ 1+ ] [ 2 + ] if ;
 
-: random-bits ( m -- n )
-    #! Top bit is always set
-    2^ [ random ] keep -1 shift bitor ; foldable
+: random-bits ( m -- n ) 2^ random ; foldable
 
 : (factor-2s) ( s n -- s n )
     dup even? [ -1 shift >r 1+ r> (factor-2s) ] when ;
@@ -32,29 +30,24 @@ SYMBOL: trials
     ] unless 0 swap (factor-2s) ;
 
 :: (miller-rabin) | n prime?! |
-    n dup 1 = over even? or [
-        drop f
-    ] [
-        1- factor-2s s set r set
-        trials get [
-            n 1- [1,b] random a set
-            a get s get n ^mod 1 = [
-                0 count set
-                r get [
-                    2^ s get * a get swap n ^mod n - -1 = [
-                        count [ 1+ ] change
-                        r get +
-                    ] when
-                ] each
-                count get zero? [
-                    f prime?!
-                    trials get +
+    n 1- factor-2s s set r set
+    trials get [
+        n 1- [1,b] random a set
+        a get s get n ^mod 1 = [
+            0 count set
+            r get [
+                2^ s get * a get swap n ^mod n - -1 = [
+                    count [ 1+ ] change
+                    r get +
                 ] when
-            ] unless
-            drop
-        ] each
-        prime?
-    ] if ;
+            ] each
+            count get zero? [
+                f prime?!
+                trials get +
+            ] when
+        ] unless
+        drop
+    ] each prime? ;
 
 TUPLE: miller-rabin-bounds ;
 
@@ -62,6 +55,7 @@ TUPLE: miller-rabin-bounds ;
     over {
         { [ dup 1 <= ] [ 3drop f ] }
         { [ dup 2 = ] [ 3drop t ] }
+        { [ dup even? ] [ 3drop f ] }
         { [ t ] [ [ drop trials set t (miller-rabin) ] with-scope ] }
     } cond ;