diff --git a/extra/math/primes/factors/factors-tests.factor b/extra/math/primes/factors/factors-tests.factor
index 70b905f4ab..f247683c1c 100644
--- a/extra/math/primes/factors/factors-tests.factor
+++ b/extra/math/primes/factors/factors-tests.factor
@@ -1,6 +1,8 @@
 USING: math.primes.factors tools.test ;
 
 { { 999983 999983 1000003 } } [ 999969000187000867 factors ] unit-test
+{ { } } [ -5 factors ] unit-test
 { { { 999983 2 } { 1000003 1 } } } [ 999969000187000867 group-factors ] unit-test
 { { 999983 1000003 } } [ 999969000187000867 unique-factors ] unit-test
 { 999967000236000612 } [ 999969000187000867 totient ] unit-test
+{ 0 } [ 1 totient ] unit-test
diff --git a/extra/math/primes/factors/factors.factor b/extra/math/primes/factors/factors.factor
index 80c93f2ae0..282c46c82e 100644
--- a/extra/math/primes/factors/factors.factor
+++ b/extra/math/primes/factors/factors.factor
@@ -1,39 +1,36 @@
-! Copyright (C) 2007 Samuel Tardieu.
+! Copyright (C) 2007-2009 Samuel Tardieu.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: arrays kernel lists make math math.primes sequences ;
 IN: math.primes.factors
 
 <PRIVATE
 
-: (factor) ( n d -- n' )
-    2dup mod zero? [ [ / ] keep dup , (factor) ] [ drop ] if ;
+: count-factor ( n d -- n' c )
+    0 [ [ 2dup mod zero? ] dip swap ] [ [ [ / ] keep ] dip 1+ ] [ ] while nip ;
+
+: (factor) ( n d -- n' ) dup [ , ] curry [ count-factor ] dip times ;
 
 : (count) ( n d -- n' )
-    [ (factor) ] { } make
-    [ [ first ] [ length ] bi 2array , ] unless-empty ;
+    dup [ swap 2array , ] curry
+    [ count-factor dup zero? [ drop ] ] dip if ;
 
 : (unique) ( n d -- n' )
-    [ (factor) ] { } make
-    [ first , ] unless-empty ;
+    dup [ , ] curry [ count-factor zero? ] dip unless ;
 
 : (factors) ( quot list n -- )
     dup 1 > [
         swap uncons swap [ pick call ] dip swap (factors)
-    ] [ 3drop ] if ;
+    ] [ 3drop ] if ; inline recursive
 
-: (decompose) ( n quot -- seq )
-    [ lprimes rot (factors) ] { } make ;
+: decompose ( n quot -- seq ) [ lprimes rot (factors) ] { } make ; inline
 
 PRIVATE>
 
-: factors ( n -- seq )
-    [ (factor) ] (decompose) ; foldable
+: factors ( n -- seq ) [ (factor) ] decompose ; flushable
 
-: group-factors ( n -- seq )
-    [ (count) ] (decompose) ; foldable
+: group-factors ( n -- seq ) [ (count) ] decompose ; flushable
 
-: unique-factors ( n -- seq )
-    [ (unique) ] (decompose) ; foldable
+: unique-factors ( n -- seq ) [ (unique) ] decompose ; flushable
 
 : totient ( n -- t )
     dup 2 < [