diff --git a/rust-version b/rust-version
index b945d0b3a26..9d2a8772234 100644
--- a/rust-version
+++ b/rust-version
@@ -1 +1 @@
-d8f50ab0ea6c529c24e575279acc72093caeb679
+374c63e0fc356eb61b1966cb6026a2a49fe9226d
diff --git a/src/bin/cargo-miri.rs b/src/bin/cargo-miri.rs
index 121930bccce..3b7af932419 100644
--- a/src/bin/cargo-miri.rs
+++ b/src/bin/cargo-miri.rs
@@ -133,11 +133,12 @@ fn test_sysroot_consistency() {
     fn get_sysroot(mut cmd: Command) -> PathBuf {
         let out = cmd.arg("--print").arg("sysroot")
             .output().expect("Failed to run rustc to get sysroot info");
-        assert!(out.status.success(), "Bad status code when getting sysroot info");
-        let sysroot = out.stdout.lines().nth(0)
-            .expect("didn't get at least one line for the sysroot").unwrap();
-        PathBuf::from(sysroot).canonicalize()
-            .expect("Failed to canonicalize sysroot")
+        let stdout = String::from_utf8(out.stdout).expect("stdout is not valid UTF-8");
+        let stderr = String::from_utf8(out.stderr).expect("stderr is not valid UTF-8");
+        let stdout = stdout.trim();
+        assert!(out.status.success(), "Bad status code when getting sysroot info.\nstdout:\n{}\nstderr:\n{}", stdout, stderr);
+        PathBuf::from(stdout).canonicalize()
+            .unwrap_or_else(|_| panic!("Failed to canonicalize sysroot: {}", stdout))
     }
 
     let rustc_sysroot = get_sysroot(Command::new("rustc"));
diff --git a/src/bin/miri-rustc-tests.rs b/src/bin/miri-rustc-tests.rs
index e8714123ceb..9b0d02f4b7e 100644
--- a/src/bin/miri-rustc-tests.rs
+++ b/src/bin/miri-rustc-tests.rs
@@ -43,7 +43,7 @@ fn after_analysis(&mut self, compiler: &interface::Compiler) -> bool {
         compiler.session().abort_if_errors();
         compiler.global_ctxt().unwrap().peek_mut().enter(|tcx| {
             if std::env::args().any(|arg| arg == "--test") {
-                struct Visitor<'tcx>(TyCtxt<'tcx, 'tcx>);
+                struct Visitor<'tcx>(TyCtxt<'tcx>);
                 impl<'tcx, 'hir> itemlikevisit::ItemLikeVisitor<'hir> for Visitor<'tcx> {
                     fn visit_item(&mut self, i: &'hir hir::Item) {
                         if let hir::ItemKind::Fn(.., body_id) = i.node {
diff --git a/src/bin/miri.rs b/src/bin/miri.rs
index 6346b2340b0..5a425baf0f6 100644
--- a/src/bin/miri.rs
+++ b/src/bin/miri.rs
@@ -102,21 +102,26 @@ fn init_late_loggers() {
 
 /// Returns the "default sysroot" that Miri will use if no `--sysroot` flag is set.
 /// Should be a compile-time constant.
-fn compile_time_sysroot() -> String {
+fn compile_time_sysroot() -> Option<String> {
+    if option_env!("RUSTC_STAGE").is_some() {
+        // This is being built as part of rustc, and gets shipped with rustup.
+        // We can rely on the sysroot computation in librustc.
+        return None;
+    }
+    // For builds outside rustc, we need to ensure that we got a sysroot
+    // that gets used as a default.  The sysroot computation in librustc would
+    // end up somewhere in the build dir.
     // Taken from PR <https://github.com/Manishearth/rust-clippy/pull/911>.
     let home = option_env!("RUSTUP_HOME").or(option_env!("MULTIRUST_HOME"));
     let toolchain = option_env!("RUSTUP_TOOLCHAIN").or(option_env!("MULTIRUST_TOOLCHAIN"));
-    match (home, toolchain) {
+    Some(match (home, toolchain) {
         (Some(home), Some(toolchain)) => format!("{}/toolchains/{}", home, toolchain),
         _ => {
             option_env!("RUST_SYSROOT")
-                .expect(
-                    "could not find sysroot. Either set `MIRI_SYSROOT` at run-time, or at \
-                     build-time specify `RUST_SYSROOT` env var or use rustup or multirust",
-                )
+                .expect("To build Miri without rustup, set the `RUST_SYSROOT` env var at build time")
                 .to_owned()
         }
-    }
+    })
 }
 
 fn main() {
@@ -165,14 +170,17 @@ fn main() {
         }
     }
 
-    // Determine sysroot.
-    let sysroot_flag = "--sysroot".to_string();
-    if !rustc_args.contains(&sysroot_flag) {
-        // We need to *always* set a --sysroot, as the "default" rustc uses is
-        // somewhere in the directory miri was built in.
-        // If no --sysroot is given, fall back to env vars that are read at *compile-time*.
-        rustc_args.push(sysroot_flag);
-        rustc_args.push(compile_time_sysroot());
+    // Determine sysroot if needed.  Make sure we always call `compile_time_sysroot`
+    // as that also does some sanity-checks of the environment we were built in.
+    // FIXME: Ideally we'd turn a bad build env into a compile-time error, but
+    // CTFE does not seem powerful enough for that yet.
+    if let Some(sysroot) = compile_time_sysroot() {
+        let sysroot_flag = "--sysroot".to_string();
+        if !rustc_args.contains(&sysroot_flag) {
+            // We need to overwrite the default that librustc would compute.
+            rustc_args.push(sysroot_flag);
+            rustc_args.push(sysroot);
+        }
     }
 
     // Finally, add the default flags all the way in the beginning, but after the binary name.
diff --git a/src/lib.rs b/src/lib.rs
index 822b173e34a..061b07478a2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -72,7 +72,7 @@ pub struct MiriConfig {
 
 // Used by priroda.
 pub fn create_ecx<'mir, 'tcx: 'mir>(
-    tcx: TyCtxt<'tcx, 'tcx>,
+    tcx: TyCtxt<'tcx>,
     main_id: DefId,
     config: MiriConfig,
 ) -> InterpResult<'tcx, InterpretCx<'mir, 'tcx, Evaluator<'tcx>>> {
@@ -212,7 +212,7 @@ pub fn create_ecx<'mir, 'tcx: 'mir>(
 }
 
 pub fn eval_main<'tcx>(
-    tcx: TyCtxt<'tcx, 'tcx>,
+    tcx: TyCtxt<'tcx>,
     main_id: DefId,
     config: MiriConfig,
 ) {
@@ -475,7 +475,7 @@ fn box_alloc(
 
     fn find_foreign_static(
         def_id: DefId,
-        tcx: TyCtxtAt<'tcx, 'tcx>,
+        tcx: TyCtxtAt<'tcx>,
     ) -> InterpResult<'tcx, Cow<'tcx, Allocation>> {
         let attrs = tcx.get_attrs(def_id);
         let link_name = match attr::first_attr_value_str_by_name(&attrs, sym::link_name) {