diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -1,3 +1,7 @@
+0.2.1.1
+-------
+* Fixed a missing case in isZero.
+
 0.2.1.0
 -------
 * Added support for converting to exact integers or exact rationals.
diff --git a/exact-pi.cabal b/exact-pi.cabal
--- a/exact-pi.cabal
+++ b/exact-pi.cabal
@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                exact-pi
-version:             0.2.1.0
+version:             0.2.1.1
 synopsis:            Exact rational multiples of pi (and integer powers of pi)
 description:         Provides an exact representation for rational multiples of pi alongside an approximate representation of all reals.
                      Useful for storing and computing with conversion factors between physical units.
diff --git a/src/Data/ExactPi.hs b/src/Data/ExactPi.hs
--- a/src/Data/ExactPi.hs
+++ b/src/Data/ExactPi.hs
@@ -47,8 +47,9 @@
 
 -- | Identifies whether an 'ExactPi' is an exact or approximate representation of zero.
 isZero :: ExactPi -> Bool
-isZero (Exact _ 0) = True
+isZero (Exact _ 0)     = True
 isZero (Approximate x) = x == (0 :: Double)
+isZero _               = False
 
 -- | Identifies whether an 'ExactPi' is an exact representation of zero.
 isExactZero :: ExactPi -> Bool