diff --git a/src/bootstrap/bin/rustc.rs b/src/bootstrap/bin/rustc.rs
index 175e32125f2..a70a15b383c 100644
--- a/src/bootstrap/bin/rustc.rs
+++ b/src/bootstrap/bin/rustc.rs
@@ -55,10 +55,10 @@ fn main() {
     } else {
         ("RUSTC_REAL", "RUSTC_LIBDIR")
     };
-    let stage = env::var("RUSTC_STAGE").unwrap();
+    let stage = env::var("RUSTC_STAGE").expect("RUSTC_STAGE was not set");
 
-    let rustc = env::var_os(rustc).unwrap();
-    let libdir = env::var_os(libdir).unwrap();
+    let rustc = env::var_os(rustc).unwrap_or_else(|| panic!("{:?} was not set", rustc));
+    let libdir = env::var_os(libdir).unwrap_or_else(|| panic!("{:?} was not set", libdir));
     let mut dylib_path = bootstrap::util::dylib_path();
     dylib_path.insert(0, PathBuf::from(libdir));
 
@@ -71,7 +71,7 @@ fn main() {
     if let Some(target) = target {
         // The stage0 compiler has a special sysroot distinct from what we
         // actually downloaded, so we just always pass the `--sysroot` option.
-        cmd.arg("--sysroot").arg(env::var_os("RUSTC_SYSROOT").unwrap());
+        cmd.arg("--sysroot").arg(env::var_os("RUSTC_SYSROOT").expect("RUSTC_SYSROOT was not set"));
 
         // When we build Rust dylibs they're all intended for intermediate
         // usage, so make sure we pass the -Cprefer-dynamic flag instead of
diff --git a/src/bootstrap/bin/rustdoc.rs b/src/bootstrap/bin/rustdoc.rs
index 79629bfd717..658ff358d62 100644
--- a/src/bootstrap/bin/rustdoc.rs
+++ b/src/bootstrap/bin/rustdoc.rs
@@ -20,15 +20,16 @@ use std::path::PathBuf;
 
 fn main() {
     let args = env::args_os().skip(1).collect::<Vec<_>>();
-    let rustdoc = env::var_os("RUSTDOC_REAL").unwrap();
-    let libdir = env::var_os("RUSTC_LIBDIR").unwrap();
+    let rustdoc = env::var_os("RUSTDOC_REAL").expect("RUSTDOC_REAL was not set");
+    let libdir = env::var_os("RUSTC_LIBDIR").expect("RUSTC_LIBDIR was not set");
+    let stage = env::var("RUSTC_STAGE").expect("RUSTC_STAGE was not set");
 
     let mut dylib_path = bootstrap::util::dylib_path();
     dylib_path.insert(0, PathBuf::from(libdir));
 
     let mut cmd = Command::new(rustdoc);
     cmd.args(&args)
-       .arg("--cfg").arg(format!("stage{}", env::var("RUSTC_STAGE").unwrap()))
+       .arg("--cfg").arg(format!("stage{}", stage))
        .arg("--cfg").arg("dox")
        .env(bootstrap::util::dylib_path_var(),
             env::join_paths(&dylib_path).unwrap());
@@ -37,4 +38,3 @@ fn main() {
         Err(e) => panic!("\n\nfailed to run {:?}: {}\n\n", cmd, e),
     })
 }
-
diff --git a/src/liballoc_jemalloc/build.rs b/src/liballoc_jemalloc/build.rs
index dc1b8d6ea98..8b31c5a5577 100644
--- a/src/liballoc_jemalloc/build.rs
+++ b/src/liballoc_jemalloc/build.rs
@@ -22,8 +22,8 @@ fn main() {
     println!("cargo:rustc-cfg=cargobuild");
     println!("cargo:rerun-if-changed=build.rs");
 
-    let target = env::var("TARGET").unwrap();
-    let host = env::var("HOST").unwrap();
+    let target = env::var("TARGET").expect("TARGET was not set");
+    let host = env::var("HOST").expect("HOST was not set");
     let build_dir = PathBuf::from(env::var_os("OUT_DIR").unwrap());
     let src_dir = env::current_dir().unwrap();
 
@@ -140,7 +140,7 @@ fn main() {
             .current_dir(&build_dir)
             .arg("build_lib_static")
             .arg("-j")
-            .arg(env::var("NUM_JOBS").unwrap()));
+            .arg(env::var("NUM_JOBS").expect("NUM_JOBS was not set")));
 
     if target.contains("windows") {
         println!("cargo:rustc-link-lib=static=jemalloc");
diff --git a/src/libcompiler_builtins/build.rs b/src/libcompiler_builtins/build.rs
index 09c400b52bc..66c683333b9 100644
--- a/src/libcompiler_builtins/build.rs
+++ b/src/libcompiler_builtins/build.rs
@@ -72,7 +72,7 @@ impl Sources {
 }
 
 fn main() {
-    let target = env::var("TARGET").unwrap();
+    let target = env::var("TARGET").expect("TARGET was not set");
     let cfg = &mut gcc::Config::new();
 
     if target.contains("msvc") {
diff --git a/src/librustc_llvm/build.rs b/src/librustc_llvm/build.rs
index ac83d860b6e..3f551476e2b 100644
--- a/src/librustc_llvm/build.rs
+++ b/src/librustc_llvm/build.rs
@@ -20,7 +20,7 @@ use build_helper::output;
 fn main() {
     println!("cargo:rustc-cfg=cargobuild");
 
-    let target = env::var("TARGET").unwrap();
+    let target = env::var("TARGET").expect("TARGET was not set");
     let llvm_config = env::var_os("LLVM_CONFIG")
                           .map(PathBuf::from)
                           .unwrap_or_else(|| {
@@ -62,8 +62,8 @@ fn main() {
     // can't trust all the output of llvm-config becaues it might be targeted
     // for the host rather than the target. As a result a bunch of blocks below
     // are gated on `if !is_crossed`
-    let target = env::var("TARGET").unwrap();
-    let host = env::var("HOST").unwrap();
+    let target = env::var("TARGET").expect("TARGET was not set");
+    let host = env::var("HOST").expect("HOST was not set");
     let is_crossed = target != host;
 
     let optional_components = ["x86", "arm", "aarch64", "mips", "powerpc", "pnacl", "systemz"];
diff --git a/src/libstd/build.rs b/src/libstd/build.rs
index 2d540c6b59a..c5732278db9 100644
--- a/src/libstd/build.rs
+++ b/src/libstd/build.rs
@@ -23,8 +23,8 @@ fn main() {
     println!("cargo:rustc-cfg=cargobuild");
     println!("cargo:rerun-if-changed=build.rs");
 
-    let target = env::var("TARGET").unwrap();
-    let host = env::var("HOST").unwrap();
+    let target = env::var("TARGET").expect("TARGET was not set");
+    let host = env::var("HOST").expect("HOST was not set");
     if cfg!(feature = "backtrace") && !target.contains("apple") && !target.contains("msvc") &&
         !target.contains("emscripten") {
         build_libbacktrace(&host, &target);
@@ -103,5 +103,5 @@ fn build_libbacktrace(host: &str, target: &str) {
     run(Command::new("make")
                 .current_dir(&build_dir)
                 .arg(format!("INCDIR={}", src_dir.display()))
-                .arg("-j").arg(env::var("NUM_JOBS").unwrap()));
+                .arg("-j").arg(env::var("NUM_JOBS").expect("NUM_JOBS was not set")));
 }
diff --git a/src/libunwind/build.rs b/src/libunwind/build.rs
index fd446f5a4f9..e1ddf8b4b7e 100644
--- a/src/libunwind/build.rs
+++ b/src/libunwind/build.rs
@@ -13,7 +13,7 @@ use std::env;
 fn main() {
     println!("cargo:rustc-cfg=cargobuild");
 
-    let target = env::var("TARGET").unwrap();
+    let target = env::var("TARGET").expect("TARGET was not set");
 
     if target.contains("linux") {
         if target.contains("musl") && !target.contains("mips") {