diff --git a/prefix-expression.cabal b/prefix-expression.cabal
--- a/prefix-expression.cabal
+++ b/prefix-expression.cabal
@@ -1,5 +1,5 @@
 name:                prefix-expression
-version:             1.0.2
+version:             1.1.0
 -- synopsis:
 description:         convert infix to prefix expression
 homepage:            https://github.com/VonFry/prefix-expression
diff --git a/src/Text/Exp/Prefix.hs b/src/Text/Exp/Prefix.hs
--- a/src/Text/Exp/Prefix.hs
+++ b/src/Text/Exp/Prefix.hs
@@ -113,7 +113,7 @@
     splitExp' sp exp
       | "" <- exp = filter (\x -> x /= "") sp
       | otherwise
-      = let match = exp =~ " +|\\( *[\\+-][0-9A-Za-z]+ *\\)|&&|\\^|\\|\\||=~|!|\\(|\\)|\\+|-|\\*|/|\\\\" :: String
+      = let match = exp =~ " +|'.*'|\".*\"|\\( *[\\+-][0-9A-Za-z]+ *\\)|&&|\\^|\\|\\||=~|!|\\(|\\)|\\+|-|\\*|/|\\\\" :: String
         in if match /= ""
            then let Just (idx, _) = elemSubIndex match exp
                     (arg, exp')   = splitAt idx exp
diff --git a/test/Text/Exp/PrefixSpec.hs b/test/Text/Exp/PrefixSpec.hs
--- a/test/Text/Exp/PrefixSpec.hs
+++ b/test/Text/Exp/PrefixSpec.hs
@@ -15,6 +15,7 @@
       fromInfix "!((1 + 3) * 3 - 4 ^ 5)" `shouldBe` Right "! - * + 1 3 3 ^ 4 5"
       fromInfix "+2 * (-1) + 3" `shouldBe` Right "+ * +2 -1 3"
       fromInfix "a + b + c" `shouldBe` Right "+ + a b c"
+      fromInfix "\"a\" + b + 'c'" `shouldBe` Right "+ + \"a\" b 'c'"
     it "failed" $ do
       (isLeft $ fromInfix "!((1 + 3) * 3 - 4 ^ 5") `shouldBe` True
       (isLeft $ fromInfix "1 + + 2") `shouldBe` True