diff --git a/src/bootstrap/bootstrap.py b/src/bootstrap/bootstrap.py
index d7ae0299dd696..762f4e653e91b 100644
--- a/src/bootstrap/bootstrap.py
+++ b/src/bootstrap/bootstrap.py
@@ -1029,7 +1029,8 @@ def build_bootstrap_cmd(self, env):
             raise Exception("no cargo executable found at `{}`".format(
                 self.cargo()))
         args = [self.cargo(), "build", "--manifest-path",
-                os.path.join(self.rust_root, "src/bootstrap/Cargo.toml")]
+                os.path.join(self.rust_root, "src/bootstrap/Cargo.toml"),
+                "-Zroot-dir="+self.rust_root]
         args.extend("--verbose" for _ in range(self.verbose))
         if self.use_locked_deps:
             args.append("--locked")
diff --git a/src/bootstrap/src/core/builder/cargo.rs b/src/bootstrap/src/core/builder/cargo.rs
index 0688a1d689282..dd138508bea62 100644
--- a/src/bootstrap/src/core/builder/cargo.rs
+++ b/src/bootstrap/src/core/builder/cargo.rs
@@ -703,6 +703,9 @@ impl Builder<'_> {
 
         cargo.arg("-j").arg(self.jobs().to_string());
 
+        // Make cargo emit diagnostics relative to the rustc src dir.
+        cargo.arg(format!("-Zroot-dir={}", self.src.display()));
+
         // FIXME: Temporary fix for https://github.com/rust-lang/cargo/issues/3005
         // Force cargo to output binaries with disambiguating hashes in the name
         let mut metadata = if compiler.stage == 0 {
diff --git a/tests/ui/extern/extern-types-field-offset.run.stderr b/tests/ui/extern/extern-types-field-offset.run.stderr
index f14073989800b..1b04b860db5a6 100644
--- a/tests/ui/extern/extern-types-field-offset.run.stderr
+++ b/tests/ui/extern/extern-types-field-offset.run.stderr
@@ -1,4 +1,4 @@
-thread 'main' panicked at core/src/panicking.rs:$LINE:$COL:
+thread 'main' panicked at library/core/src/panicking.rs:$LINE:$COL:
 attempted to compute the size or alignment of extern type `Opaque`
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 thread caused non-unwinding panic. aborting.
diff --git a/tests/ui/extern/extern-types-size_of_val.align.run.stderr b/tests/ui/extern/extern-types-size_of_val.align.run.stderr
index faad1aa13faf6..20c4d8785e846 100644
--- a/tests/ui/extern/extern-types-size_of_val.align.run.stderr
+++ b/tests/ui/extern/extern-types-size_of_val.align.run.stderr
@@ -1,4 +1,4 @@
-thread 'main' panicked at core/src/panicking.rs:$LINE:$COL:
+thread 'main' panicked at library/core/src/panicking.rs:$LINE:$COL:
 attempted to compute the size or alignment of extern type `A`
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 thread caused non-unwinding panic. aborting.
diff --git a/tests/ui/extern/extern-types-size_of_val.size.run.stderr b/tests/ui/extern/extern-types-size_of_val.size.run.stderr
index faad1aa13faf6..20c4d8785e846 100644
--- a/tests/ui/extern/extern-types-size_of_val.size.run.stderr
+++ b/tests/ui/extern/extern-types-size_of_val.size.run.stderr
@@ -1,4 +1,4 @@
-thread 'main' panicked at core/src/panicking.rs:$LINE:$COL:
+thread 'main' panicked at library/core/src/panicking.rs:$LINE:$COL:
 attempted to compute the size or alignment of extern type `A`
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 thread caused non-unwinding panic. aborting.
diff --git a/tests/ui/panics/panic-in-cleanup.run.stderr b/tests/ui/panics/panic-in-cleanup.run.stderr
index 3417d4bf1a300..e7def11b0e948 100644
--- a/tests/ui/panics/panic-in-cleanup.run.stderr
+++ b/tests/ui/panics/panic-in-cleanup.run.stderr
@@ -4,6 +4,6 @@ note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 thread 'main' panicked at $DIR/panic-in-cleanup.rs:16:9:
 BOOM
 stack backtrace:
-thread 'main' panicked at core/src/panicking.rs:$LINE:$COL:
+thread 'main' panicked at library/core/src/panicking.rs:$LINE:$COL:
 panic in a destructor during cleanup
 thread caused non-unwinding panic. aborting.
diff --git a/tests/ui/panics/panic-in-ffi.run.stderr b/tests/ui/panics/panic-in-ffi.run.stderr
index 58f5187f0daf5..fe8c2b04b91a5 100644
--- a/tests/ui/panics/panic-in-ffi.run.stderr
+++ b/tests/ui/panics/panic-in-ffi.run.stderr
@@ -2,7 +2,7 @@ thread 'main' panicked at $DIR/panic-in-ffi.rs:21:5:
 Test
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 Noisy Drop
-thread 'main' panicked at core/src/panicking.rs:$LINE:$COL:
+thread 'main' panicked at library/core/src/panicking.rs:$LINE:$COL:
 panic in a function that cannot unwind
 stack backtrace:
 thread caused non-unwinding panic. aborting.
diff --git a/tests/ui/process/println-with-broken-pipe.run.stderr b/tests/ui/process/println-with-broken-pipe.run.stderr
index f9d138a042414..a334c0ad20473 100644
--- a/tests/ui/process/println-with-broken-pipe.run.stderr
+++ b/tests/ui/process/println-with-broken-pipe.run.stderr
@@ -1,3 +1,3 @@
-thread 'main' panicked at std/src/io/stdio.rs:LL:CC:
+thread 'main' panicked at library/std/src/io/stdio.rs:LL:CC:
 failed printing to stdout: Broken pipe (os error 32)
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace