diff --git a/tests/compiletest.rs b/tests/compiletest.rs
index b64b091bf6ff..435ad0f51a27 100644
--- a/tests/compiletest.rs
+++ b/tests/compiletest.rs
@@ -3,26 +3,32 @@ extern crate compiletest_rs as compiletest;
 use std::path::PathBuf;
 
 fn run_mode(mode: &'static str) {
+    // Disable rustc's new error fomatting. It breaks these tests.
+    std::env::remove_var("RUST_NEW_ERROR_FORMAT");
+
+    // Taken from 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"));
+    let sysroot = match (home, toolchain) {
+        (Some(home), Some(toolchain)) => format!("{}/toolchains/{}", home, toolchain),
+        _ => option_env!("RUST_SYSROOT")
+            .expect("need to specify RUST_SYSROOT env var or use rustup or multirust")
+            .to_owned(),
+    };
+    let sysroot_flag = format!("--sysroot {}", sysroot);
+
     // FIXME: read directories in sysroot/lib/rustlib and generate the test targets from that
     let targets = &["x86_64-unknown-linux-gnu", "i686-unknown-linux-gnu"];
 
     for &target in targets {
         let mut config = compiletest::default_config();
+        config.host_rustcflags = Some(sysroot_flag.clone());
+        config.mode = mode.parse().ok().expect("Invalid mode");
+        config.run_lib_path = format!("{}/lib/rustlib/{}/lib", sysroot, target);
         config.rustc_path = "target/debug/miri".into();
-        let path = std::env::var("RUST_SYSROOT").expect("env variable `RUST_SYSROOT` not set");
-        config.run_lib_path = format!("{}/lib/rustlib/{}/lib", path, target);
-        let path = format!("--sysroot {}", path);
-        config.target_rustcflags = Some(path.clone());
-        config.host_rustcflags = Some(path);
-        let cfg_mode = mode.parse().ok().expect("Invalid mode");
-
-        config.mode = cfg_mode;
         config.src_base = PathBuf::from(format!("tests/{}", mode));
         config.target = target.to_owned();
-
-        // Disable rustc's new error fomatting. It breaks these tests.
-        std::env::remove_var("RUST_NEW_ERROR_FORMAT");
-
+        config.target_rustcflags = Some(sysroot_flag.clone());
         compiletest::run_tests(&config);
     }
 }