diff --git a/src/bootstrap/src/core/build_steps/llvm.rs b/src/bootstrap/src/core/build_steps/llvm.rs
index dbd4f1c814055..ae86874cc99ae 100644
--- a/src/bootstrap/src/core/build_steps/llvm.rs
+++ b/src/bootstrap/src/core/build_steps/llvm.rs
@@ -773,7 +773,15 @@ fn configure_cmake(
         .define("CMAKE_CXX_COMPILER", sanitize_cc(&cxx))
         .define("CMAKE_ASM_COMPILER", sanitize_cc(&cc));
 
-    cfg.build_arg("-j").build_arg(builder.jobs().to_string());
+    // If we are running under a FIFO jobserver, we should not pass -j to CMake; otherwise it
+    // overrides the jobserver settings and can lead to oversubscription.
+    let has_modern_jobserver = env::var("MAKEFLAGS")
+        .map(|flags| flags.contains("--jobserver-auth=fifo:"))
+        .unwrap_or(false);
+
+    if !has_modern_jobserver {
+        cfg.build_arg("-j").build_arg(builder.jobs().to_string());
+    }
     let mut cflags = ccflags.cflags.clone();
     // FIXME(madsmtm): Allow `cmake-rs` to select flags by itself by passing
     // our flags via `.cflag`/`.cxxflag` instead.
diff --git a/src/bootstrap/src/core/builder/cargo.rs b/src/bootstrap/src/core/builder/cargo.rs
index 7150b2b0d59f2..f08632d979051 100644
--- a/src/bootstrap/src/core/builder/cargo.rs
+++ b/src/bootstrap/src/core/builder/cargo.rs
@@ -547,9 +547,17 @@ impl Builder<'_> {
             assert_eq!(target, compiler.host);
         }
 
-        // Remove make-related flags to ensure Cargo can correctly set things up
-        cargo.env_remove("MAKEFLAGS");
-        cargo.env_remove("MFLAGS");
+        // Bootstrap only supports modern FIFO jobservers. Older pipe-based jobservers can run into
+        // "invalid file descriptor" errors, as the jobserver file descriptors are not inherited by
+        // scripts like bootstrap.py, while the environment variable is propagated. So, we pass
+        // MAKEFLAGS only if we detect a FIFO jobserver, otherwise we clear it.
+        let has_modern_jobserver = env::var("MAKEFLAGS")
+            .map(|flags| flags.contains("--jobserver-auth=fifo:"))
+            .unwrap_or(false);
+
+        if !has_modern_jobserver {
+            cargo.env_remove("MAKEFLAGS");
+        }
 
         cargo
     }