diff --git a/basis/compiler/tree/modular-arithmetic/authors.txt b/basis/compiler/tree/modular-arithmetic/authors.txt
new file mode 100644
index 0000000000..a44f8d7f8d
--- /dev/null
+++ b/basis/compiler/tree/modular-arithmetic/authors.txt
@@ -0,0 +1,2 @@
+Slava Pestov
+Daniel Ehrenberg
diff --git a/basis/compiler/tree/modular-arithmetic/modular-arithmetic-tests.factor b/basis/compiler/tree/modular-arithmetic/modular-arithmetic-tests.factor
index 55a8cb9ea2..7fb1b3d5ac 100644
--- a/basis/compiler/tree/modular-arithmetic/modular-arithmetic-tests.factor
+++ b/basis/compiler/tree/modular-arithmetic/modular-arithmetic-tests.factor
@@ -1,3 +1,5 @@
+! Copyright (C) 2008, 2009 Slava Pestov, Daniel Ehrenberg.
+! See http://factorcode.org/license.txt for BSD license.
 IN: compiler.tree.modular-arithmetic.tests
 USING: kernel kernel.private tools.test math math.partial-dispatch
 math.private accessors slots.private sequences strings sbufs
diff --git a/basis/compiler/tree/modular-arithmetic/modular-arithmetic.factor b/basis/compiler/tree/modular-arithmetic/modular-arithmetic.factor
index 6ddefa9307..148286faba 100644
--- a/basis/compiler/tree/modular-arithmetic/modular-arithmetic.factor
+++ b/basis/compiler/tree/modular-arithmetic/modular-arithmetic.factor
@@ -1,4 +1,4 @@
-! Copyright (C) 2008 Slava Pestov.
+! Copyright (C) 2008, 2009 Slava Pestov, Daniel Ehrenberg.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: math math.partial-dispatch namespaces sequences sets
 accessors assocs words kernel memoize fry combinators