diff --git a/src/cargo/core/resolver/encode.rs b/src/cargo/core/resolver/encode.rs
index 344082bf60e..5bfc6a8c8b7 100644
--- a/src/cargo/core/resolver/encode.rs
+++ b/src/cargo/core/resolver/encode.rs
@@ -14,7 +14,7 @@ use super::Resolve;
 #[derive(Serialize, Deserialize, Debug)]
 pub struct EncodableResolve {
     package: Option<Vec<EncodableDependency>>,
-    /// `root` is optional to allow forward compatibility.
+    /// `root` is optional to allow backward compatibility.
     root: Option<EncodableDependency>,
     metadata: Option<Metadata>,
 
@@ -311,7 +311,6 @@ impl<'de> de::Deserialize<'de> for EncodablePackageId {
 pub struct WorkspaceResolve<'a, 'cfg: 'a> {
     pub ws: &'a Workspace<'cfg>,
     pub resolve: &'a Resolve,
-    pub use_root_key: bool,
 }
 
 impl<'a, 'cfg> ser::Serialize for WorkspaceResolve<'a, 'cfg> {
@@ -321,15 +320,7 @@ impl<'a, 'cfg> ser::Serialize for WorkspaceResolve<'a, 'cfg> {
         let mut ids: Vec<&PackageId> = self.resolve.graph.iter().collect();
         ids.sort();
 
-        let root = self.ws.members().max_by_key(|member| {
-            member.name()
-        }).map(Package::package_id);
-
         let encodable = ids.iter().filter_map(|&id| {
-            if self.use_root_key && root.unwrap() == id {
-                return None
-            }
-
             Some(encodable_resolve_node(id, self.resolve))
         }).collect::<Vec<_>>();
 
@@ -347,11 +338,6 @@ impl<'a, 'cfg> ser::Serialize for WorkspaceResolve<'a, 'cfg> {
 
         let metadata = if metadata.is_empty() { None } else { Some(metadata) };
 
-        let root = match root {
-            Some(root) if self.use_root_key => Some(encodable_resolve_node(root, self.resolve)),
-            _ => None,
-        };
-
         let patch = Patch {
             unused: self.resolve.unused_patches().iter().map(|id| {
                 EncodableDependency {
@@ -365,7 +351,7 @@ impl<'a, 'cfg> ser::Serialize for WorkspaceResolve<'a, 'cfg> {
         };
         EncodableResolve {
             package: Some(encodable),
-            root: root,
+            root: None,
             metadata: metadata,
             patch: patch,
         }.serialize(s)
diff --git a/src/cargo/ops/lockfile.rs b/src/cargo/ops/lockfile.rs
index 64de6f1ea37..8dc5b45672e 100644
--- a/src/cargo/ops/lockfile.rs
+++ b/src/cargo/ops/lockfile.rs
@@ -40,30 +40,13 @@ pub fn write_pkg_lockfile(ws: &Workspace, resolve: &Resolve) -> CargoResult<()>
         Ok(s)
     });
 
-    // Forward compatibility: if `orig` uses rootless format
-    // from the future, do the same.
-    let use_root_key = if let Ok(ref orig) = orig {
-        !orig.starts_with("[[package]]")
-    } else {
-        true
-    };
-
     let toml = toml::Value::try_from(WorkspaceResolve {
         ws: ws,
         resolve: resolve,
-        use_root_key: use_root_key,
     }).unwrap();
 
     let mut out = String::new();
 
-    // Note that we do not use e.toml.to_string() as we want to control the
-    // exact format the toml is in to ensure pretty diffs between updates to the
-    // lockfile.
-    if let Some(root) = toml.get("root") {
-        out.push_str("[root]\n");
-        emit_package(root.as_table().unwrap(), &mut out);
-    }
-
     let deps = toml["package"].as_array().unwrap();
     for dep in deps.iter() {
         let dep = dep.as_table().unwrap();
diff --git a/src/doc/book/src/guide/cargo-toml-vs-cargo-lock.md b/src/doc/book/src/guide/cargo-toml-vs-cargo-lock.md
index de3f18cb08b..574a6677f23 100644
--- a/src/doc/book/src/guide/cargo-toml-vs-cargo-lock.md
+++ b/src/doc/book/src/guide/cargo-toml-vs-cargo-lock.md
@@ -71,7 +71,7 @@ Cargo will take the latest commit and write that information out into our
 `Cargo.lock` when we build for the first time. That file will look like this:
 
 ```toml
-[root]
+[[package]]
 name = "hello_world"
 version = "0.1.0"
 dependencies = [
diff --git a/src/doc/guide.md b/src/doc/guide.md
index 55decf1ac6a..e63be4dd592 100644
--- a/src/doc/guide.md
+++ b/src/doc/guide.md
@@ -328,7 +328,7 @@ Cargo will take the latest commit and write that information out into our
 `Cargo.lock` when we build for the first time. That file will look like this:
 
 ```toml
-[root]
+[[package]]
 name = "hello_world"
 version = "0.1.0"
 dependencies = [
diff --git a/tests/bad-config.rs b/tests/bad-config.rs
index cff576dbb47..06e58100559 100644
--- a/tests/bad-config.rs
+++ b/tests/bad-config.rs
@@ -256,7 +256,7 @@ fn duplicate_packages_in_cargo_lock() {
         "#)
         .file("src/lib.rs", "")
         .file("Cargo.lock", r#"
-            [root]
+            [[package]]
             name = "bar"
             version = "0.0.1"
             dependencies = [
@@ -300,7 +300,7 @@ fn bad_source_in_cargo_lock() {
         "#)
         .file("src/lib.rs", "")
         .file("Cargo.lock", r#"
-            [root]
+            [[package]]
             name = "bar"
             version = "0.0.1"
             dependencies = [
@@ -334,7 +334,7 @@ fn bad_dependency_in_lockfile() {
         "#)
         .file("src/lib.rs", "")
         .file("Cargo.lock", r#"
-            [root]
+            [[package]]
             name = "foo"
             version = "0.0.1"
             dependencies = [
diff --git a/tests/generate-lockfile.rs b/tests/generate-lockfile.rs
index 94432e4f645..2151f45e51c 100644
--- a/tests/generate-lockfile.rs
+++ b/tests/generate-lockfile.rs
@@ -145,7 +145,7 @@ fn preserve_line_endings_issue_2076() {
 
     let lock0 = p.read_lockfile();
 
-    assert!(lock0.starts_with("[root]\n"));
+    assert!(lock0.starts_with("[[package]]\n"));
 
     let lock1 = lock0.replace("\n", "\r\n");
     {
@@ -157,7 +157,7 @@ fn preserve_line_endings_issue_2076() {
 
     let lock2 = p.read_lockfile();
 
-    assert!(lock2.starts_with("[root]\r\n"));
+    assert!(lock2.starts_with("[[package]]\r\n"));
     assert_eq!(lock1, lock2);
 }
 
diff --git a/tests/git.rs b/tests/git.rs
index ca0f209f39f..7328a1e56ae 100644
--- a/tests/git.rs
+++ b/tests/git.rs
@@ -971,7 +971,7 @@ fn stale_cached_version() {
     let rev = repo.revparse_single("HEAD").unwrap().id();
 
     File::create(&foo.root().join("Cargo.lock")).unwrap().write_all(format!(r#"
-        [root]
+        [[package]]
         name = "foo"
         version = "0.0.0"
         dependencies = [
diff --git a/tests/install.rs b/tests/install.rs
index 3ed4bf0d9a5..a753697afcd 100644
--- a/tests/install.rs
+++ b/tests/install.rs
@@ -829,7 +829,7 @@ fn git_with_lockfile() {
         "#)
         .file("bar/src/lib.rs", "fn main() {}")
         .file("Cargo.lock", r#"
-            [root]
+            [[package]]
             name = "foo"
             version = "0.1.0"
             dependencies = [ "bar 0.1.0" ]
diff --git a/tests/lockfile-compat.rs b/tests/lockfile-compat.rs
index 00eacebbfcb..d9f6791687c 100644
--- a/tests/lockfile-compat.rs
+++ b/tests/lockfile-compat.rs
@@ -8,9 +8,36 @@ use hamcrest::assert_that;
 
 #[test]
 fn oldest_lockfile_still_works() {
+    let cargo_commands = vec![
+        "build",
+        "update"
+    ];
+    for cargo_command in cargo_commands {
+        oldest_lockfile_still_works_with_command(cargo_command);
+    }
+}
+
+fn oldest_lockfile_still_works_with_command(cargo_command: &str) {
     Package::new("foo", "0.1.0").publish();
 
-    let lockfile = r#"
+    let expected_lockfile =
+r#"[[package]]
+name = "bar"
+version = "0.0.1"
+dependencies = [
+ "foo 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "foo"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[metadata]
+"checksum foo 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "[..]"
+"#;
+
+    let old_lockfile = r#"
 [root]
 name = "bar"
 version = "0.0.1"
@@ -35,14 +62,19 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
             foo = "0.1.0"
         "#)
         .file("src/lib.rs", "")
-        .file("Cargo.lock", lockfile);
+        .file("Cargo.lock", old_lockfile);
+
     p.build();
 
-    assert_that(p.cargo("build"),
+    assert_that(p.cargo(cargo_command),
                 execs().with_status(0));
 
     let lock = p.read_lockfile();
-    assert!(lock.starts_with(lockfile.trim()));
+    for (l, r) in expected_lockfile.lines().zip(lock.lines()) {
+        assert!(lines_match(l, r), "Lines differ:\n{}\n\n{}", l, r);
+    }
+
+    assert_eq!(lock.lines().count(), expected_lockfile.lines().count());
 }
 
 #[test]
@@ -61,7 +93,7 @@ fn totally_wild_checksums_works() {
         "#)
         .file("src/lib.rs", "")
         .file("Cargo.lock", r#"
-[root]
+[[package]]
 name = "bar"
 version = "0.0.1"
 dependencies = [
@@ -85,7 +117,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
     let lock = p.read_lockfile();
     assert!(lock.starts_with(r#"
-[root]
+[[package]]
 name = "bar"
 version = "0.0.1"
 dependencies = [
@@ -117,7 +149,7 @@ fn wrong_checksum_is_an_error() {
         "#)
         .file("src/lib.rs", "")
         .file("Cargo.lock", r#"
-[root]
+[[package]]
 name = "bar"
 version = "0.0.1"
 dependencies = [
@@ -170,7 +202,7 @@ fn unlisted_checksum_is_bad_if_we_calculate() {
         "#)
         .file("src/lib.rs", "")
         .file("Cargo.lock", r#"
-[root]
+[[package]]
 name = "bar"
 version = "0.0.1"
 dependencies = [
@@ -230,7 +262,7 @@ fn listed_checksum_bad_if_we_cannot_compute() {
         "#, git.url()))
         .file("src/lib.rs", "")
         .file("Cargo.lock", &format!(r#"
-[root]
+[[package]]
 name = "bar"
 version = "0.0.1"
 dependencies = [
@@ -287,7 +319,7 @@ fn current_lockfile_format() {
     let actual = p.read_lockfile();
 
     let expected = "\
-[root]
+[[package]]
 name = \"bar\"
 version = \"0.0.1\"
 dependencies = [
diff --git a/tests/overrides.rs b/tests/overrides.rs
index 0941f774dea..0a022650f67 100644
--- a/tests/overrides.rs
+++ b/tests/overrides.rs
@@ -802,7 +802,7 @@ fn override_an_override() {
             "serde:0.8.0" = { path = "serde" }
         "#)
         .file("Cargo.lock", r#"
-            [root]
+            [[package]]
             name = "local"
             version = "0.0.1"
             dependencies = [
diff --git a/tests/workspaces.rs b/tests/workspaces.rs
index 68e9468f008..2e2dc1b32a1 100644
--- a/tests/workspaces.rs
+++ b/tests/workspaces.rs
@@ -961,7 +961,7 @@ fn lockfile_can_specify_nonexistant_members() {
         "#)
         .file("a/src/main.rs", "fn main() {}")
         .file("Cargo.lock", r#"
-            [root]
+            [[package]]
             name = "a"
             version = "0.1.0"