diff --git a/cyclotomic.cabal b/cyclotomic.cabal
--- a/cyclotomic.cabal
+++ b/cyclotomic.cabal
@@ -1,6 +1,6 @@
 Name:                cyclotomic
-Version:             0.5.1
-Stability:           experimental
+Version:             1.0
+Stability:           stable
 Synopsis:            A subfield of the complex numbers for exact calculation.
 Description:         The cyclotomic numbers are a subset of the
                      complex numbers that are represented exactly, enabling exact
@@ -17,12 +17,11 @@
 License-file:        LICENSE
 Author:              Scott N. Walck
 Maintainer:          Scott N. Walck <walck@lvc.edu>
-Copyright:           (c) Scott N. Walck 2012-2017
+Copyright:           (c) Scott N. Walck 2012-2019
 Category:            Math
 Build-type:          Simple
 Extra-source-files:  test/Properties.hs
 Cabal-version:       >= 1.10
-Tested-with:         GHC == 7.8.4, GHC == 7.10.2,  GHC == 7.10.3,  GHC == 8.0.1
 Bug-reports:         https://github.com/walck/cyclotomic/issues
 
 Test-suite cyclotomic-tests
@@ -38,7 +37,7 @@
 Library
   ghc-options:       -Wall
   Exposed-modules:   Data.Complex.Cyclotomic, Data.Number.RealCyclotomic
-  Build-depends:     base >= 4.2 && < 4.12,
+  Build-depends:     base >= 4.2 && < 4.13,
                      containers >= 0.3,
                      arithmoi >= 0.4
   default-language:  Haskell2010
diff --git a/src/Data/Number/RealCyclotomic.hs b/src/Data/Number/RealCyclotomic.hs
--- a/src/Data/Number/RealCyclotomic.hs
+++ b/src/Data/Number/RealCyclotomic.hs
@@ -63,6 +63,7 @@
     , isRat
     , toRat
     , toReal
+    , magSq
     , goldenRatio
     , heron
     )
@@ -147,3 +148,7 @@
     = sqrtRat (s * (s-a) * (s-b) * (s-c))
       where
         s = (a + b + c) / 2
+
+-- | The square of the magnitude of a real cyclotomic.
+magSq :: RealCyclotomic -> RealCyclotomic
+magSq (RealCyclotomic c) = RealCyclotomic (c * Cyc.conj c)