diff --git a/extra/project-euler/common/common-tests.factor b/extra/project-euler/common/common-tests.factor
new file mode 100644
index 0000000000..1f7a3668e2
--- /dev/null
+++ b/extra/project-euler/common/common-tests.factor
@@ -0,0 +1,17 @@
+! Copyright (C) 2009 Doug Coleman.
+! See http://factorcode.org/license.txt for BSD license.
+USING: tools.test project-euler.common ;
+IN: project-euler.common.tests
+
+[ 4 ] [ -1000 number-length ] unit-test
+[ 3 ] [ -999 number-length ] unit-test
+[ 3 ] [ -100 number-length ] unit-test
+[ 2 ] [ -99 number-length ] unit-test
+[ 1 ] [ -9 number-length ] unit-test
+[ 1 ] [ -1 number-length ] unit-test
+[ 1 ] [ 0 number-length ] unit-test
+[ 1 ] [ 9 number-length ] unit-test
+[ 2 ] [ 99 number-length ] unit-test
+[ 3 ] [ 100 number-length ] unit-test
+[ 3 ] [ 999 number-length ] unit-test
+[ 4 ] [ 1000 number-length ] unit-test
diff --git a/extra/project-euler/common/common.factor b/extra/project-euler/common/common.factor
index efec77355b..3d320fad62 100644
--- a/extra/project-euler/common/common.factor
+++ b/extra/project-euler/common/common.factor
@@ -76,7 +76,12 @@ PRIVATE>
     [ dup 0 = not ] [ 10 /mod ] produce reverse nip ;
 
 : number-length ( n -- m )
-    log10 floor 1 + >integer ;
+    abs [
+        1
+    ] [
+        1 0 [ 2over >= ]
+        [ [ 10 * ] [ 1 + ] bi* ] while 2nip
+    ] if-zero ;
 
 : nth-prime ( n -- n )
     1 - lprimes lnth ;