diff --git a/Data/Attoparsec/ByteString/Char8.hs b/Data/Attoparsec/ByteString/Char8.hs
index b4f6b57..6330eaa 100644
--- a/Data/Attoparsec/ByteString/Char8.hs
+++ b/Data/Attoparsec/ByteString/Char8.hs
@@ -151,8 +151,8 @@ import qualified Data.Attoparsec.Internal as I
 import qualified Data.ByteString as B8
 import qualified Data.ByteString.Char8 as B
 
-instance (a ~ B.ByteString) => IsString (Parser a) where
-    fromString = I.string . B.pack
+instance a ~ () => IsString (Parser a) where
+    fromString = void . I.string . B.pack
 
 -- $encodings
 --
diff --git a/Data/Attoparsec/Text/Internal.hs b/Data/Attoparsec/Text/Internal.hs
index 02f04fd..eaee966 100644
--- a/Data/Attoparsec/Text/Internal.hs
+++ b/Data/Attoparsec/Text/Internal.hs
@@ -66,7 +66,7 @@ module Data.Attoparsec.Text.Internal
     ) where
 
 import Control.Applicative ((<|>), (<$>), pure, (*>))
-import Control.Monad (when)
+import Control.Monad (void, when)
 import Data.Attoparsec.Combinator ((<?>))
 import Data.Attoparsec.Internal
 import Data.Attoparsec.Internal.Types hiding (Parser, Failure, Success)
@@ -88,8 +88,8 @@ type Result = IResult Text
 type Failure r = T.Failure Text Buffer r
 type Success a r = T.Success Text Buffer a r
 
-instance (a ~ Text) => IsString (Parser a) where
-    fromString = string . T.pack
+instance a ~ () => IsString (Parser a) where
+    fromString = void . string . T.pack
 
 -- | The parser @satisfy p@ succeeds for any character for which the
 -- predicate @p@ returns 'True'. Returns the character that is
diff --git a/attoparsec.cabal b/attoparsec.cabal
index 6793556..b3ace6e 100644
--- a/attoparsec.cabal
+++ b/attoparsec.cabal
@@ -1,7 +1,7 @@
 cabal-version:   2.0
   -- 2.0 needed for internal libraries
 name:            attoparsec
-version:         0.14.4
+version:         0.15.0
 license:         BSD3
 license-file:    LICENSE
 category:        Text, Parsing
diff --git a/benchmarks/Genome.hs b/benchmarks/Genome.hs
index 8a6e3b1..605487a 100644
--- a/benchmarks/Genome.hs
+++ b/benchmarks/Genome.hs
@@ -44,13 +44,13 @@ genome = bgroup "genome" [
         geneTL = rechunkT 4 geneT
 
 searchBS :: B.Parser ByteString
-searchBS = "caac" *> ("aaca" <|> "aact")
+searchBS = "caac" *> (B.string "aaca" <|> B.string "aact")
 
 searchBSCI :: B.Parser ByteString
 searchBSCI = B.stringCI "CAAC" *> (B.stringCI "AACA" <|> B.stringCI "AACT")
 
 searchT :: T.Parser Text
-searchT = "caac" *> ("aaca" <|> "aact")
+searchT = "caac" *> (T.string "aaca" <|> T.string "aact")
 
 searchTCI :: T.Parser Text
 searchTCI = T.asciiCI "CAAC" *> (T.asciiCI "AACA" <|> T.asciiCI "AACT")
diff --git a/changelog.md b/changelog.md
index 086eac8..e52a110 100644
--- a/changelog.md
+++ b/changelog.md
@@ -1,3 +1,9 @@
+# 0.15.0
+
+* Change equational constraints:
+  - `a ~ Text => IsString (Parser a)` to `a ~ () => IsString (Parser a)`
+  - `a ~ ByteString => IsString (Parser a)` to `a ~ () => IsString (Parser a)`
+
 # 0.14.4
 
 * Fix a segmentation fault when built against `text-2.0`
diff --git a/tests/QC/Simple.hs b/tests/QC/Simple.hs
index 45975b6..062ad36 100644
--- a/tests/QC/Simple.hs
+++ b/tests/QC/Simple.hs
@@ -18,7 +18,7 @@ import qualified Data.Attoparsec.ByteString.Char8 as A
 t_issue75 = expect issue75 "ab" (A.Done "" "b")
 
 issue75 :: A.Parser ByteString
-issue75 = "a" >> ("b" <|> "")
+issue75 = "a" >> (A.string "b" <|> A.string "")
 
 expect :: (Show r, Eq r) => A.Parser r -> ByteString -> A.Result r -> Property
 expect p input wanted =