diff --git a/src/rustup-mock/src/mock_bin_src.rs b/src/rustup-mock/src/mock_bin_src.rs
index 993ad4b308..0fa58193cf 100644
--- a/src/rustup-mock/src/mock_bin_src.rs
+++ b/src/rustup-mock/src/mock_bin_src.rs
@@ -14,34 +14,6 @@ fn main() {
             let mut hash_file = PathBuf::from(format!("{}.version-hash", me.display()));
             let mut version = String::new();
             let mut hash = String::new();
-            if !version_file.exists() {
-                // There's a "MAJOR HACKS" statement in `toolchain.rs` right
-                // now where custom toolchains use a `cargo.exe` that's
-                // temporarily located elsewhere so they can execute the correct
-                // `rustc.exe`. This means that our dummy version files may not
-                // be just next to use.
-                //
-                // Detect this here and work around it.
-                assert!(cfg!(windows));
-                assert!(env::var_os("RUSTUP_TOOLCHAIN").is_some());
-                let mut alt = me.clone();
-                alt.pop(); // remove our filename
-                assert!(alt.ends_with("fallback"));
-                alt.pop(); // pop 'fallback'
-                alt.push("toolchains");
-
-                let mut part = PathBuf::from("bin");
-                part.push(me.file_name().unwrap());
-
-                let path = alt.read_dir().unwrap()
-                    .map(|e| e.unwrap().path().join(&part))
-                    .filter(|p| p.exists())
-                    .find(|p| equivalent(&p, &me))
-                    .unwrap();
-
-                version_file = format!("{}.version", path.display()).into();
-                hash_file = format!("{}.version-hash", path.display()).into();
-            }
             File::open(&version_file).unwrap().read_to_string(&mut version).unwrap();
             File::open(&hash_file).unwrap().read_to_string(&mut hash).unwrap();
             println!("{} ({})", version, hash);
@@ -57,9 +29,9 @@ fn main() {
         }
         Some("--call-rustc") => {
             // Used by the fallback_cargo_calls_correct_rustc test. Tests that
-            // the environment has been set up right such that invoking rustc
-            // will actually invoke the wrapper
-            let rustc = &format!("rustc{}", EXE_SUFFIX);
+            // the environment has been set up right such that invoking cargo
+            // will invoke the correct rustc executable.
+            let rustc = env::var_os("RUSTC").unwrap_or(format!("rustc{}", EXE_SUFFIX).into());
             Command::new(rustc).arg("--version").status().unwrap();
         }
         _ => panic!("bad mock proxy commandline"),
diff --git a/src/rustup/toolchain.rs b/src/rustup/toolchain.rs
index 3cb1e5610f..7ec5f05592 100644
--- a/src/rustup/toolchain.rs
+++ b/src/rustup/toolchain.rs
@@ -373,38 +373,26 @@ impl<'a> Toolchain<'a> {
             return Err(ErrorKind::ToolchainNotInstalled(primary_toolchain.name.to_owned()).into());
         }
 
-        let src_file = self.path.join("bin").join(format!("cargo{}", EXE_SUFFIX));
-
-        // MAJOR HACKS: Copy cargo.exe to its own directory on windows before
-        // running it. This is so that the fallback cargo, when it in turn runs
-        // rustc.exe, will run the rustc.exe out of the PATH environment
-        // variable, _not_ the rustc.exe sitting in the same directory as the
-        // fallback. See the `fallback_cargo_calls_correct_rustc` testcase and
-        // PR 812.
+        let exe_path = self.path.join("bin").join(format!("cargo{}", EXE_SUFFIX));
+
+        let mut cmd = Command::new(exe_path);
+        self.set_env(&mut cmd);
+        cmd.env("RUSTUP_TOOLCHAIN", &primary_toolchain.name);
+
+        // Set the RUSTC environment variable to the primary toolchain binary
+        // on Windows. This is so that the fallback cargo will run that executable
+        // and _not_ the rustc.exe sitting in the same directory. See the
+        // `fallback_cargo_calls_correct_rustc` testcase.
         //
         // On Windows, spawning a process will search the running application's
         // directory for the exe to spawn before searching PATH, and we don't want
         // it to do that, because cargo's directory contains the _wrong_ rustc. See
         // the documantation for the lpCommandLine argument of CreateProcess.
-        let exe_path = if cfg!(windows) {
-            use std::fs;
-            let fallback_dir = self.cfg.rustup_dir.join("fallback");
-            fs::create_dir_all(&fallback_dir)
-                .chain_err(|| "unable to create dir to hold fallback exe")?;
-            let fallback_file = fallback_dir.join("cargo.exe");
-            if fallback_file.exists() {
-                fs::remove_file(&fallback_file)
-                    .chain_err(|| "unable to unlink old fallback exe")?;
+        if cfg!(windows) {
+            if env::var_os("RUSTC").is_none() {
+                cmd.env("RUSTC", primary_toolchain.binary_file("rustc"));
             }
-            fs::hard_link(&src_file, &fallback_file)
-                .chain_err(|| "unable to hard link fallback exe")?;
-            fallback_file
-        } else {
-            src_file
-        };
-        let mut cmd = Command::new(exe_path);
-        self.set_env(&mut cmd);
-        cmd.env("RUSTUP_TOOLCHAIN", &primary_toolchain.name);
+        }
         Ok(cmd)
     }