diff --git a/src/docker.rs b/src/docker.rs
index 3dbf6a962..5c41dc69c 100644
--- a/src/docker.rs
+++ b/src/docker.rs
@@ -32,6 +32,7 @@ pub struct RustEnv<'a> {
     pub rustup_home: (PathBuf, Perm),
     pub target_dir: (PathBuf, Perm),
     pub cap_lints: &'a ExCapLints,
+    pub enable_unstable_cargo_features: bool,
 }
 
 pub struct MountConfig<'a> {
@@ -97,7 +98,7 @@ pub fn rust_container(config: RustEnv) -> ContainerConfig {
         },
     ];
 
-    let env = vec![
+    let mut env = vec![
         ("USER_ID", format!("{}", user_id())),
         ("CMD", config.args.join(" ")),
         ("CARGO_INCREMENTAL", "0".to_string()),
@@ -107,6 +108,12 @@ pub fn rust_container(config: RustEnv) -> ContainerConfig {
             format!("--cap-lints={}", config.cap_lints.to_str()),
         ),
     ];
+    if config.enable_unstable_cargo_features {
+        env.push((
+            "__CARGO_TEST_CHANNEL_OVERRIDE_DO_NOT_USE_THIS",
+            "nightly".to_string(),
+        ));
+    }
 
     ContainerConfig {
         image_name: IMAGE_NAME,
diff --git a/src/ex.rs b/src/ex.rs
index 68f2a13c1..02db4b0e3 100644
--- a/src/ex.rs
+++ b/src/ex.rs
@@ -374,7 +374,12 @@ fn capture_lockfile_inner(
     path: &Path,
     toolchain: &Toolchain,
 ) -> Result<()> {
-    let args = &["generate-lockfile", "--manifest-path", "Cargo.toml"];
+    let args = &[
+        "generate-lockfile",
+        "--manifest-path",
+        "Cargo.toml",
+        "-Zno-index-update",
+    ];
     toolchain
         .run_cargo(ex, path, args, CargoState::Unlocked, false)
         .chain_err(|| format!("unable to generate lockfile for {}", krate))?;
diff --git a/src/toolchain.rs b/src/toolchain.rs
index b8db4c667..0325d2f22 100644
--- a/src/toolchain.rs
+++ b/src/toolchain.rs
@@ -44,6 +44,8 @@ impl Toolchain {
             }
         }
 
+        self.prep_offline_registry()?;
+
         Ok(())
     }
 
@@ -90,6 +92,10 @@ impl Toolchain {
             CargoState::Locked => docker::Perm::ReadOnly,
             CargoState::Unlocked => docker::Perm::ReadWrite,
         };
+
+        let enable_unstable_cargo_features =
+            !toolchain_name.starts_with("nightly-") && args.iter().any(|a| a.starts_with("-Z"));
+
         let rust_env = docker::RustEnv {
             args: &full_args,
             work_dir: (source_dir.into(), perm),
@@ -98,9 +104,27 @@ impl Toolchain {
             // This is configured as CARGO_TARGET_DIR by the docker container itself
             target_dir: (ex_target_dir, docker::Perm::ReadWrite),
             cap_lints: &ex.cap_lints,
+            enable_unstable_cargo_features,
         };
         docker::run(&docker::rust_container(rust_env), quiet)
     }
+
+    pub fn prep_offline_registry(&self) -> Result<()> {
+        // This nop cargo command is to update the registry
+        // so we don't have to do it for each crate.
+        let toolchain_arg = "+".to_string() + &self.rustup_name();
+        let full_args = [&toolchain_arg, "search", "lazy_static"];
+        RunCommand::new(&installed_binary("cargo"), &full_args)
+            .local_rustup()
+            .quiet(true)
+            .run()
+            .chain_err(|| {
+                format!(
+                    "unable to update the index for toolchain {}",
+                    &self.rustup_name()
+                )
+            })
+    }
 }
 
 impl ToString for Toolchain {