diff --git a/Cargo.lock b/Cargo.lock
index 67d44569..6f8cafa4 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -534,7 +534,7 @@ dependencies = [
  "shlex 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "staticfile 0.5.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "tempfile 3.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "toml 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "toml 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "toml-query 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "walkdir 2.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "ws 0.7.8 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1209,7 +1209,7 @@ dependencies = [
 
 [[package]]
 name = "toml"
-version = "0.4.6"
+version = "0.4.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "serde 1.0.72 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1224,7 +1224,7 @@ dependencies = [
  "is-match 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "regex 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "toml 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "toml 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -1558,7 +1558,7 @@ dependencies = [
 "checksum textwrap 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)" = "307686869c93e71f94da64286f9a9524c0f308a9e1c87a583de8e9c9039ad3f6"
 "checksum thread_local 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)" = "c6b53e329000edc2b34dbe8545fd20e55a333362d0a321909685a19bd28c3f1b"
 "checksum time 0.1.40 (registry+https://github.com/rust-lang/crates.io-index)" = "d825be0eb33fda1a7e68012d51e9c7f451dc1a69391e7fdc197060bb8c56667b"
-"checksum toml 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)" = "a0263c6c02c4db6c8f7681f9fd35e90de799ebd4cfdeab77a38f4ff6b3d8c0d9"
+"checksum toml 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)" = "4a2ecc31b0351ea18b3fe11274b8db6e4d82bce861bbb22e6dbed40417902c65"
 "checksum toml-query 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ab234a943a2363ad774020e2f9474a38a85bc4396bace01a96380144aef17db3"
 "checksum traitobject 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "efd1f82c56340fdf16f2a953d7bda4f8fdffba13d93b00844c25572110b26079"
 "checksum typeable 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "1410f6f91f21d1612654e7cc69193b0334f909dcf2c790c4826254fbb86f8887"
diff --git a/Cargo.toml b/Cargo.toml
index d47f682e..1e0d1447 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -26,7 +26,7 @@ pulldown-cmark = "0.1.2"
 lazy_static = "1.0"
 log = "0.4"
 env_logger = "0.5"
-toml = "0.4"
+toml = "0.4.8"
 memchr = "2.0"
 open = "1.1"
 regex = "1.0.0"
diff --git a/src/preprocess/cmd.rs b/src/preprocess/cmd.rs
index 4398eba6..59b0cdd3 100644
--- a/src/preprocess/cmd.rs
+++ b/src/preprocess/cmd.rs
@@ -65,9 +65,13 @@ impl CmdPreprocessor {
         }
     }
 
-    fn write_input<W: Write>(&self, writer: W, book: &Book, ctx: &PreprocessorContext) -> Result<()> {
-        serde_json::to_writer(writer, &(ctx, book))
-            .map_err(Into::into)
+    fn write_input<W: Write>(
+        &self,
+        writer: W,
+        book: &Book,
+        ctx: &PreprocessorContext,
+    ) -> Result<()> {
+        serde_json::to_writer(writer, &(ctx, book)).map_err(Into::into)
     }
 
     /// The command this `Preprocessor` will invoke.
@@ -105,7 +109,12 @@ impl Preprocessor for CmdPreprocessor {
             .stdout(Stdio::piped())
             .stderr(Stdio::inherit())
             .spawn()
-            .chain_err(|| format!("Unable to start the \"{}\" preprocessor. Is it installed?", self.name()))?;
+            .chain_err(|| {
+                format!(
+                    "Unable to start the \"{}\" preprocessor. Is it installed?",
+                    self.name()
+                )
+            })?;
 
         self.write_input_to_child(&mut child, &book, ctx);
 
@@ -114,13 +123,21 @@ impl Preprocessor for CmdPreprocessor {
             .chain_err(|| "Error waiting for the preprocessor to complete")?;
 
         trace!("{} exited with output: {:?}", self.cmd, output);
-        ensure!(output.status.success(), "The preprocessor exited unsuccessfully");
+        ensure!(
+            output.status.success(),
+            "The preprocessor exited unsuccessfully"
+        );
 
-        serde_json::from_slice(&output.stdout).chain_err(|| "Unable to parse the preprocessed book")
+        serde_json::from_slice(&output.stdout)
+            .chain_err(|| "Unable to parse the preprocessed book")
     }
 
     fn supports_renderer(&self, renderer: &str) -> bool {
-        debug!("Checking if the \"{}\" preprocessor supports \"{}\"", self.name(), renderer);
+        debug!(
+            "Checking if the \"{}\" preprocessor supports \"{}\"",
+            self.name(),
+            renderer
+        );
 
         let mut cmd = match self.command() {
             Ok(c) => c,
@@ -152,3 +169,36 @@ impl Preprocessor for CmdPreprocessor {
         outcome.unwrap_or(false)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::path::Path;
+    use MDBook;
+
+    fn book_example() -> MDBook {
+        let example =
+            Path::new(env!("CARGO_MANIFEST_DIR")).join("book-example");
+        MDBook::load(example).unwrap()
+    }
+
+    #[test]
+    fn round_trip_write_and_parse_input() {
+        let cmd = CmdPreprocessor::new("test".to_string(), "test".to_string());
+        let md = book_example();
+        let ctx = PreprocessorContext::new(
+            md.root.clone(),
+            md.config.clone(),
+            "some-renderer".to_string(),
+        );
+
+        let mut buffer = Vec::new();
+        cmd.write_input(&mut buffer, &md.book, &ctx).unwrap();
+
+        let (got_ctx, got_book) =
+            CmdPreprocessor::parse_input(buffer.as_slice()).unwrap();
+
+        assert_eq!(got_book, md.book);
+        assert_eq!(got_ctx, ctx);
+    }
+}