diff --git a/src/tools/compiletest/src/directives/auxiliary.rs b/src/tools/compiletest/src/directives/auxiliary.rs
index 1b72931949c5..1d5b7926a8e3 100644
--- a/src/tools/compiletest/src/directives/auxiliary.rs
+++ b/src/tools/compiletest/src/directives/auxiliary.rs
@@ -6,12 +6,20 @@ use std::iter;
 use super::directives::{AUX_BIN, AUX_BUILD, AUX_CODEGEN_BACKEND, AUX_CRATE, PROC_MACRO};
 use crate::common::Config;
 use crate::directives::DirectiveLine;
+use crate::util::static_regex;
+
+#[cfg(test)]
+mod tests;
 
 /// The value of an `aux-crate` directive.
-#[derive(Clone, Debug, Default)]
+#[derive(Clone, Debug, Default, PartialEq, Eq)]
 pub struct AuxCrate {
+    /// Contains `--extern` modifiers, if any. See the tracking issue for more
+    /// info: <https://github.com/rust-lang/rust/issues/98405>
+    /// With `aux-crate: noprelude:foo=bar.rs` this will be `noprelude`.
+    pub extern_modifiers: Option<String>,
     /// With `aux-crate: foo=bar.rs` this will be `foo`.
-    /// With `aux-crate: noprelude:foo=bar.rs` this will be `noprelude:foo`.
+    /// With `aux-crate: noprelude:foo=bar.rs` this will be `foo`.
     pub name: String,
     /// With `aux-crate: foo=bar.rs` this will be `bar.rs`.
     pub path: String,
@@ -74,9 +82,20 @@ pub(super) fn parse_and_update_aux(
 }
 
 fn parse_aux_crate(r: String) -> AuxCrate {
-    let mut parts = r.trim().splitn(2, '=');
-    AuxCrate {
-        name: parts.next().expect("missing aux-crate name (e.g. log=log.rs)").to_string(),
-        path: parts.next().expect("missing aux-crate value (e.g. log=log.rs)").to_string(),
-    }
+    let r = r.trim();
+
+    // Matches:
+    //   name=path
+    //   modifiers:name=path
+    let caps = static_regex!(r"^(?:(?<modifiers>[^=]*?):)?(?<name>[^=]*)=(?<path>.*)$")
+        .captures(r)
+        .unwrap_or_else(|| {
+            panic!("couldn't parse aux-crate value `{r}` (should be e.g. `log=log.rs`)")
+        });
+
+    let modifiers = caps.name("modifiers").map(|m| m.as_str().to_string());
+    let name = caps["name"].to_string();
+    let path = caps["path"].to_string();
+
+    AuxCrate { extern_modifiers: modifiers, name, path }
 }
diff --git a/src/tools/compiletest/src/directives/auxiliary/tests.rs b/src/tools/compiletest/src/directives/auxiliary/tests.rs
new file mode 100644
index 000000000000..ad205eaabfda
--- /dev/null
+++ b/src/tools/compiletest/src/directives/auxiliary/tests.rs
@@ -0,0 +1,27 @@
+use super::*;
+
+#[test]
+fn test_aux_crate_value_no_modifiers() {
+    assert_eq!(
+        AuxCrate { extern_modifiers: None, name: "foo".to_string(), path: "foo.rs".to_string() },
+        parse_aux_crate("foo=foo.rs".to_string())
+    );
+}
+
+#[test]
+fn test_aux_crate_value_with_modifiers() {
+    assert_eq!(
+        AuxCrate {
+            extern_modifiers: Some("noprelude".to_string()),
+            name: "foo".to_string(),
+            path: "foo.rs".to_string()
+        },
+        parse_aux_crate("noprelude:foo=foo.rs".to_string())
+    );
+}
+
+#[test]
+#[should_panic(expected = "couldn't parse aux-crate value `foo.rs` (should be e.g. `log=log.rs`)")]
+fn test_aux_crate_value_invalid() {
+    parse_aux_crate("foo.rs".to_string());
+}
diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 901ce8421ebf..dfbe84d5da72 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -1277,23 +1277,36 @@ impl<'test> TestCx<'test> {
                 .replace('-', "_")
         };
 
-        let add_extern =
-            |rustc: &mut Command, aux_name: &str, aux_path: &str, aux_type: AuxType| {
-                let lib_name = get_lib_name(&path_to_crate_name(aux_path), aux_type);
-                if let Some(lib_name) = lib_name {
-                    rustc.arg("--extern").arg(format!("{}={}/{}", aux_name, aux_dir, lib_name));
-                }
-            };
+        let add_extern = |rustc: &mut Command,
+                          extern_modifiers: Option<&str>,
+                          aux_name: &str,
+                          aux_path: &str,
+                          aux_type: AuxType| {
+            let lib_name = get_lib_name(&path_to_crate_name(aux_path), aux_type);
+            if let Some(lib_name) = lib_name {
+                let modifiers_and_name = match extern_modifiers {
+                    Some(modifiers) => format!("{modifiers}:{aux_name}"),
+                    None => aux_name.to_string(),
+                };
+                rustc.arg("--extern").arg(format!("{modifiers_and_name}={aux_dir}/{lib_name}"));
+            }
+        };
 
-        for AuxCrate { name, path } in &self.props.aux.crates {
+        for AuxCrate { extern_modifiers, name, path } in &self.props.aux.crates {
             let aux_type = self.build_auxiliary(&path, &aux_dir, None);
-            add_extern(rustc, name, path, aux_type);
+            add_extern(rustc, extern_modifiers.as_deref(), name, path, aux_type);
         }
 
         for proc_macro in &self.props.aux.proc_macros {
             self.build_auxiliary(proc_macro, &aux_dir, Some(AuxType::ProcMacro));
             let crate_name = path_to_crate_name(proc_macro);
-            add_extern(rustc, &crate_name, proc_macro, AuxType::ProcMacro);
+            add_extern(
+                rustc,
+                None, // `extern_modifiers`
+                &crate_name,
+                proc_macro,
+                AuxType::ProcMacro,
+            );
         }
 
         // Build any `//@ aux-codegen-backend`, and pass the resulting library