diff --git a/src/bin/miri.rs b/src/bin/miri.rs
index 379f25ef757..56c2e433d06 100644
--- a/src/bin/miri.rs
+++ b/src/bin/miri.rs
@@ -21,7 +21,10 @@ impl<'a> CompilerCalls<'a> for MiriCompilerCalls {
         let mut control = CompileController::basic();
         control.after_hir_lowering.callback = Box::new(after_hir_lowering);
         control.after_analysis.callback = Box::new(after_analysis);
-        control.after_analysis.stop = Compilation::Stop;
+        if std::env::var("MIRI_HOST_TARGET") != Ok("yes".to_owned()) {
+            // only fully compile targets on the host
+            control.after_analysis.stop = Compilation::Stop;
+        }
         control
     }
 }
@@ -136,6 +139,12 @@ fn main() {
         args.push(sysroot_flag);
         args.push(find_sysroot());
     }
+    // we run the optimization passes inside miri
+    // if we ran them twice we'd get funny failures due to borrowck ElaborateDrops only working on
+    // unoptimized MIR
+    // FIXME: add an after-mir-passes hook to rustc driver
+    args.push("-Zmir-opt-level=0".to_owned());
+    // for auxilary builds in unit tests
     args.push("-Zalways-encode-mir".to_owned());
 
     rustc_driver::run_compiler(&args, &mut MiriCompilerCalls, None, None);
diff --git a/tests/compiletest.rs b/tests/compiletest.rs
index 50970086ee5..90a40d8e39b 100644
--- a/tests/compiletest.rs
+++ b/tests/compiletest.rs
@@ -27,13 +27,20 @@ fn run_pass() {
     compiletest::run_tests(&config);
 }
 
-fn miri_pass(path: &str, target: &str) {
+fn miri_pass(path: &str, target: &str, host: &str) {
     let mut config = compiletest::default_config();
     config.mode = "mir-opt".parse().expect("Invalid mode");
     config.src_base = PathBuf::from(path);
     config.target = target.to_owned();
     config.rustc_path = PathBuf::from("target/debug/miri");
+    // don't actually execute the final binary, it might be for other targets and we only care
+    // about running miri, not the binary.
+    config.runtool = Some("echo \"\" || ".to_owned());
+    if target == host {
+        std::env::set_var("MIRI_HOST_TARGET", "yes");
+    }
     compiletest::run_tests(&config);
+    std::env::set_var("MIRI_HOST_TARGET", "");
 }
 
 fn is_target_dir<P: Into<PathBuf>>(path: P) -> bool {
@@ -65,10 +72,11 @@ fn compile_test() {
             .to_owned(),
     };
     run_pass();
+    let host = toolchain.unwrap().splitn(2, '-').skip(1).next().unwrap();
     for_all_targets(&sysroot, |target| {
-        miri_pass("tests/run-pass", &target);
+        miri_pass("tests/run-pass", &target, host);
         if let Ok(path) = std::env::var("MIRI_RUSTC_TEST") {
-            miri_pass(&path, &target);
+            miri_pass(&path, &target, host);
         }
     });
     compile_fail(&sysroot);
diff --git a/tests/run-pass/aux_test.rs b/tests/run-pass/aux_test.rs
index 5510582e87a..1b1dbaa6838 100644
--- a/tests/run-pass/aux_test.rs
+++ b/tests/run-pass/aux_test.rs
@@ -1,9 +1,8 @@
 // aux-build:dep.rs
+// ignore-cross-compile
 
-// FIXME: Auxiliary builds are currently broken.
-// extern crate dep;
+extern crate dep;
 
 fn main() {
-    // FIXME: Auxiliary builds are currently broken.
-    // dep::foo();
+    dep::foo();
 }