diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Revision history for replace-megaparsec
 
+## 1.4.3.0 -- 2020-09-28
+
+Bugfix sepCap backtracking when sep fails
+
+See [#33](https://github.com/jamesdbrock/replace-megaparsec/issues/33)
+
 ## 1.4.1.0 -- 2020-05-07
 
 anyTill use getInput instead of takeRest
diff --git a/replace-megaparsec.cabal b/replace-megaparsec.cabal
--- a/replace-megaparsec.cabal
+++ b/replace-megaparsec.cabal
@@ -1,5 +1,5 @@
 name:                replace-megaparsec
-version:             1.4.2.0
+version:             1.4.3.0
 cabal-version:       1.18
 synopsis:            Find, replace, and split string patterns with Megaparsec parsers (instead of regex)
 homepage:            https://github.com/jamesdbrock/replace-megaparsec
diff --git a/src/Replace/Megaparsec.hs b/src/Replace/Megaparsec.hs
--- a/src/Replace/Megaparsec.hs
+++ b/src/Replace/Megaparsec.hs
@@ -199,7 +199,7 @@
 -- input == 'Data.Monoid.mconcat' ('Data.Bifunctor.second' 'Data.Tuple.fst' '<$>' output)
 -- @
 splitCap
-    :: forall e s a. (Ord e, Stream s, Tokens s ~ s)
+    :: forall e s a. (Ord e, Show e, Show (Token s), Stream s, Tokens s ~ s)
     => Parsec e s a
         -- ^ The pattern matching parser @sep@
     -> s
@@ -208,7 +208,7 @@
         -- ^ List of matching and non-matching input sections.
 splitCap sep input = do
     case runParser (sepCap sep) "" input of
-        (Left _) -> undefined -- sepCap can never fail
+        (Left (ParseErrorBundle errs _)) -> error (show errs) -- undefined -- sepCap can never fail
         (Right r) -> r
 {-# INLINABLE splitCap #-}
 
diff --git a/src/Replace/Megaparsec/Internal/ByteString.hs b/src/Replace/Megaparsec/Internal/ByteString.hs
--- a/src/Replace/Megaparsec/Internal/ByteString.hs
+++ b/src/Replace/Megaparsec/Internal/ByteString.hs
@@ -49,7 +49,7 @@
                 -- the Maybe then the benchmarks get dramatically worse.
                 thisiter <- (<|>)
                     ( do
-                        x <- sep
+                        x <- try sep
                         restAfter <- getInput
                         -- Don't allow a match of a zero-width pattern
                         when (B.length restAfter >= B.length restThis) empty
@@ -86,7 +86,7 @@
   where
     go = do
       end <- getInput
-      r <- optional sep
+      r <- optional $ try sep
       case r of
         Nothing -> anySingle >> go
         Just x -> pure (end, x)
diff --git a/src/Replace/Megaparsec/Internal/Text.hs b/src/Replace/Megaparsec/Internal/Text.hs
--- a/src/Replace/Megaparsec/Internal/Text.hs
+++ b/src/Replace/Megaparsec/Internal/Text.hs
@@ -50,7 +50,7 @@
                 -- the Maybe then the benchmarks get dramatically worse.
                 thisiter <- (<|>)
                     ( do
-                        x <- sep
+                        x <- try sep
                         restAfter@(Text _ _ afterLen) <- getInput
                         -- Don't allow a match of a zero-width pattern
                         when (afterLen >= thisLen) empty
@@ -87,7 +87,7 @@
   where
     go = do
       (Text _ _ thisLen) <- getInput
-      r <- optional sep
+      r <- optional $ try sep
       case r of
         Nothing -> anySingle >> go
         Just x -> pure (thisLen, x)
diff --git a/tests/TestText.hs b/tests/TestText.hs
--- a/tests/TestText.hs
+++ b/tests/TestText.hs
@@ -68,6 +68,10 @@
     , Test $ breakCapTest "zero-width" (lookAhead (upperChar :: Parser Char)) "aAa" (Just ("a", 'A', "Aa"))
     , Test $ breakCapTest "empty input" (upperChar :: Parser Char) "" Nothing
     , Test $ breakCapTest "empty input zero-width" (return () :: Parser ()) "" (Just ("", (), ""))
+    -- I was unable to write a failing test for
+    -- https://github.com/jamesdbrock/replace-megaparsec/issues/33
+    -- but adding this "sep backtrack" test anyway
+    , Test $ splitCapTest "sep backtrack" (match $ between (string "{{") (string "}}") (T.pack <$> many (alphaNumChar <|> spaceChar) :: Parser T.Text)) "{{foo.}}" [Left "{{foo.}}"]
     ]
   where
     runParserTest nam p input expected = TestInstance
@@ -106,6 +110,19 @@
                     else return (Finished $ TestSuite.Fail
                                 $ "got " <> show output <> " expected " <> show expected)
             , name = "breakCap " ++ nam
+            , tags = []
+            , options = []
+            , setOption = \_ _ -> Left "no options supported"
+            }
+
+    splitCapTest nam sep input expected = TestInstance
+            { run = do
+                let output = splitCap sep input
+                if (output == expected)
+                    then return (Finished Pass)
+                    else return (Finished $ TestSuite.Fail
+                                $ "got " <> show output <> " expected " <> show expected)
+            , name = "splitCap " ++ nam
             , tags = []
             , options = []
             , setOption = \_ _ -> Left "no options supported"