diff --git a/book-example/src/cli/build.md b/book-example/src/cli/build.md
index fd584e18..5d218b66 100644
--- a/book-example/src/cli/build.md
+++ b/book-example/src/cli/build.md
@@ -29,8 +29,9 @@ your default web browser after building it.
 #### --dest-dir
 
 The `--dest-dir` (`-d`) option allows you to change the output directory for the
-book. If not specified it will default to the value of the `build.build-dir` key
-in `book.toml`, or to `./book` relative to the book's root directory.
+book. Relative paths are interpreted relative to the book's root directory. If
+not specified it will default to the value of the `build.build-dir` key in
+`book.toml`, or to `./book`.
 
 -------------------
 
diff --git a/book-example/src/cli/clean.md b/book-example/src/cli/clean.md
index 7482e0d5..23efc450 100644
--- a/book-example/src/cli/clean.md
+++ b/book-example/src/cli/clean.md
@@ -19,9 +19,9 @@ mdbook clean path/to/book
 #### --dest-dir
 
 The `--dest-dir` (`-d`) option allows you to override the book's output
-directory, which will be deleted by this command. If not specified it will
-default to the value of the `build.build-dir` key in `book.toml`, or to `./book`
-relative to the book's root directory.
+directory, which will be deleted by this command. Relative paths are interpreted
+relative to the book's root directory. If not specified it will default to the
+value of the `build.build-dir` key in `book.toml`, or to `./book`.
 
 ```bash
 mdbook clean --dest-dir=path/to/book
diff --git a/book-example/src/cli/serve.md b/book-example/src/cli/serve.md
index cfc3beec..96c7443a 100644
--- a/book-example/src/cli/serve.md
+++ b/book-example/src/cli/serve.md
@@ -40,8 +40,9 @@ default web browser after starting the server.
 #### --dest-dir
 
 The `--dest-dir` (`-d`) option allows you to change the output directory for the
-book. If not specified it will default to the value of the `build.build-dir` key
-in `book.toml`, or to `./book` relative to the book's root directory.
+book. Relative paths are interpreted relative to the book's root directory. If
+not specified it will default to the value of the `build.build-dir` key in
+`book.toml`, or to `./book`.
 
 -----
 
diff --git a/book-example/src/cli/test.md b/book-example/src/cli/test.md
index b558d6b4..c13e8809 100644
--- a/book-example/src/cli/test.md
+++ b/book-example/src/cli/test.md
@@ -48,5 +48,6 @@ comma-delimited list (`-L foo,bar`).
 #### --dest-dir
 
 The `--dest-dir` (`-d`) option allows you to change the output directory for the
-book. If not specified it will default to the value of the `build.build-dir` key
-in `book.toml`, or to `./book` relative to the book's root directory.
+book. Relative paths are interpreted relative to the book's root directory. If
+not specified it will default to the value of the `build.build-dir` key in
+`book.toml`, or to `./book`.
diff --git a/book-example/src/cli/watch.md b/book-example/src/cli/watch.md
index 33cfcd7e..68dcd562 100644
--- a/book-example/src/cli/watch.md
+++ b/book-example/src/cli/watch.md
@@ -22,5 +22,6 @@ your default web browser.
 #### --dest-dir
 
 The `--dest-dir` (`-d`) option allows you to change the output directory for the
-book. If not specified it will default to the value of the `build.build-dir` key
-in `book.toml`, or to `./book` relative to the book's root directory.
+book. Relative paths are interpreted relative to the book's root directory. If
+not specified it will default to the value of the `build.build-dir` key in
+`book.toml`, or to `./book`.
diff --git a/src/cmd/build.rs b/src/cmd/build.rs
index f4c0cecd..4a5abbc0 100644
--- a/src/cmd/build.rs
+++ b/src/cmd/build.rs
@@ -9,7 +9,8 @@ pub fn make_subcommand<'a, 'b>() -> App<'a, 'b> {
         .about("Builds a book from its markdown files")
         .arg_from_usage(
             "-d, --dest-dir=[dest-dir] 'Output directory for the book{n}\
-             (If omitted, uses build.build-dir from book.toml or defaults to ./book)'",
+             Relative paths are interpreted relative to the book's root directory.{n}\
+             If omitted, mdBook uses build.build-dir from book.toml or defaults to `./book`.'",
         ).arg_from_usage(
             "[dir] 'Root directory for the book{n}\
              (Defaults to the Current Directory when omitted)'",
diff --git a/src/cmd/clean.rs b/src/cmd/clean.rs
index 09c8d912..fba49be8 100644
--- a/src/cmd/clean.rs
+++ b/src/cmd/clean.rs
@@ -10,7 +10,9 @@ pub fn make_subcommand<'a, 'b>() -> App<'a, 'b> {
         .about("Deletes a built book")
         .arg_from_usage(
             "-d, --dest-dir=[dest-dir] 'Output directory for the book{n}\
-             (If omitted, uses build.build-dir from book.toml or defaults to ./book)'",
+             Relative paths are interpreted relative to the book's root directory.{n}\
+             Running this command deletes this directory.{n}\
+             If omitted, mdBook uses build.build-dir from book.toml or defaults to `./book`.'",
         ).arg_from_usage(
             "[dir] 'Root directory for the book{n}\
              (Defaults to the Current Directory when omitted)'",
diff --git a/src/cmd/serve.rs b/src/cmd/serve.rs
index aefd21ed..ba89c587 100644
--- a/src/cmd/serve.rs
+++ b/src/cmd/serve.rs
@@ -22,7 +22,8 @@ pub fn make_subcommand<'a, 'b>() -> App<'a, 'b> {
         .about("Serves a book at http://localhost:3000, and rebuilds it on changes")
         .arg_from_usage(
             "-d, --dest-dir=[dest-dir] 'Output directory for the book{n}\
-             (If omitted, uses build.build-dir from book.toml or defaults to ./book)'",
+             Relative paths are interpreted relative to the book's root directory.{n}\
+             If omitted, mdBook uses build.build-dir from book.toml or defaults to `./book`.'",
         )
         .arg_from_usage(
             "[dir] 'Root directory for the book{n}\
diff --git a/src/cmd/test.rs b/src/cmd/test.rs
index e215f028..63e1910d 100644
--- a/src/cmd/test.rs
+++ b/src/cmd/test.rs
@@ -9,7 +9,8 @@ pub fn make_subcommand<'a, 'b>() -> App<'a, 'b> {
         .about("Tests that a book's Rust code samples compile")
         .arg_from_usage(
             "-d, --dest-dir=[dest-dir] 'Output directory for the book{n}\
-             (If omitted, uses build.build-dir from book.toml or defaults to ./book)'",
+             Relative paths are interpreted relative to the book's root directory.{n}\
+             If omitted, mdBook uses build.build-dir from book.toml or defaults to `./book`.'",
         )
         .arg_from_usage(
             "[dir] 'Root directory for the book{n}\
diff --git a/src/cmd/watch.rs b/src/cmd/watch.rs
index 1aaa633c..d800ae7d 100644
--- a/src/cmd/watch.rs
+++ b/src/cmd/watch.rs
@@ -16,7 +16,8 @@ pub fn make_subcommand<'a, 'b>() -> App<'a, 'b> {
         .about("Watches a book's files and rebuilds it on changes")
         .arg_from_usage(
             "-d, --dest-dir=[dest-dir] 'Output directory for the book{n}\
-             (If omitted, uses build.build-dir from book.toml or defaults to ./book)'",
+             Relative paths are interpreted relative to the book's root directory.{n}\
+             If omitted, mdBook uses build.build-dir from book.toml or defaults to `./book`.'",
         ).arg_from_usage(
             "[dir] 'Root directory for the book{n}\
              (Defaults to the Current Directory when omitted)'",