diff --git a/build.rs b/build.rs
index 257487848..ea757bfd4 100644
--- a/build.rs
+++ b/build.rs
@@ -1,6 +1,6 @@
 #![allow(clippy::uninlined_format_args)]
 
-use fish_build_helper::{fish_build_dir, workspace_root};
+use fish_build_helper::{env_var, fish_build_dir, workspace_root};
 use rsconf::Target;
 use std::env;
 use std::path::{Path, PathBuf};
@@ -30,9 +30,9 @@ fn main() {
     );
 
     // Some build info
-    rsconf::set_env_value("BUILD_TARGET_TRIPLE", &env::var("TARGET").unwrap());
-    rsconf::set_env_value("BUILD_HOST_TRIPLE", &env::var("HOST").unwrap());
-    rsconf::set_env_value("BUILD_PROFILE", &env::var("PROFILE").unwrap());
+    rsconf::set_env_value("BUILD_TARGET_TRIPLE", &env_var("TARGET").unwrap());
+    rsconf::set_env_value("BUILD_HOST_TRIPLE", &env_var("HOST").unwrap());
+    rsconf::set_env_value("BUILD_PROFILE", &env_var("PROFILE").unwrap());
 
     let version = &get_version(&env::current_dir().unwrap());
     // Per https://doc.rust-lang.org/cargo/reference/build-scripts.html#inputs-to-the-build-script,
@@ -114,7 +114,7 @@ fn detect_apple(_: &Target) -> bool {
 
 fn detect_cygwin(_: &Target) -> bool {
     // Cygwin target is usually cross-compiled.
-    std::env::var("CARGO_CFG_TARGET_OS").unwrap() == "cygwin"
+    env_var("CARGO_CFG_TARGET_OS").unwrap() == "cygwin"
 }
 
 /// Detect if we're being compiled for a BSD-derived OS, allowing targeting code conditionally with
@@ -126,7 +126,7 @@ fn detect_cygwin(_: &Target) -> bool {
 fn detect_bsd(_: &Target) -> bool {
     // Instead of using `uname`, we can inspect the TARGET env variable set by Cargo. This lets us
     // support cross-compilation scenarios.
-    let mut target = std::env::var("TARGET").unwrap();
+    let mut target = env_var("TARGET").unwrap();
     if !target.chars().all(|c| c.is_ascii_lowercase()) {
         target = target.to_ascii_lowercase();
     }
@@ -178,14 +178,14 @@ fn setup_paths() {
     use unix_path::{Path, PathBuf};
 
     fn get_path(name: &str, default: &str, onvar: &Path) -> PathBuf {
-        let mut var = PathBuf::from(env::var(name).unwrap_or(default.to_string()));
+        let mut var = PathBuf::from(env_var(name).unwrap_or(default.to_string()));
         if var.is_relative() {
             var = onvar.join(var);
         }
         var
     }
 
-    let prefix = PathBuf::from(env::var("PREFIX").unwrap_or("/usr/local".to_string()));
+    let prefix = PathBuf::from(env_var("PREFIX").unwrap_or("/usr/local".to_string()));
     rsconf::rebuild_if_env_changed("PREFIX");
     rsconf::set_env_value("PREFIX", prefix.to_str().unwrap());
 
@@ -229,7 +229,7 @@ fn get_version(src_dir: &Path) -> String {
     use std::fs::read_to_string;
     use std::process::Command;
 
-    if let Ok(var) = std::env::var("FISH_BUILD_VERSION") {
+    if let Some(var) = env_var("FISH_BUILD_VERSION") {
         return var;
     }
 
diff --git a/crates/build-helper/src/lib.rs b/crates/build-helper/src/lib.rs
index 0831823c4..df9baf1b1 100644
--- a/crates/build-helper/src/lib.rs
+++ b/crates/build-helper/src/lib.rs
@@ -1,4 +1,21 @@
-use std::{borrow::Cow, env, path::Path};
+use std::{borrow::Cow, env, os::unix::ffi::OsStrExt, path::Path};
+
+pub fn env_var(name: &str) -> Option<String> {
+    let err = match env::var(name) {
+        Ok(p) => return Some(p),
+        Err(err) => err,
+    };
+    use env::VarError::*;
+    match err {
+        NotPresent => None,
+        NotUnicode(os_string) => {
+            panic!(
+                "Environment variable {name} is not valid Unicode: {:?}",
+                os_string.as_bytes()
+            )
+        }
+    }
+}
 
 pub fn workspace_root() -> &'static Path {
     let manifest_dir = Path::new(env!("CARGO_MANIFEST_DIR"));
diff --git a/crates/build-man-pages/build.rs b/crates/build-man-pages/build.rs
index 0492ea68c..1cb097d04 100644
--- a/crates/build-man-pages/build.rs
+++ b/crates/build-man-pages/build.rs
@@ -14,12 +14,9 @@ fn main() {
 
 #[cfg(not(clippy))]
 fn build_man(man_dir: &Path) {
-    use std::{
-        env,
-        process::{Command, Stdio},
-    };
+    use std::process::{Command, Stdio};
 
-    use fish_build_helper::workspace_root;
+    use fish_build_helper::{env_var, workspace_root};
 
     let workspace_root = workspace_root();
 
@@ -47,7 +44,7 @@ fn build_man(man_dir: &Path) {
     let _ = std::fs::create_dir_all(sec1_str);
 
     rsconf::rebuild_if_env_changed("FISH_BUILD_DOCS");
-    if env::var("FISH_BUILD_DOCS") == Ok("0".to_string()) {
+    if env_var("FISH_BUILD_DOCS") == Some("0".to_string()) {
         rsconf::warn!("Skipping man pages because $FISH_BUILD_DOCS is set to 0");
         return;
     }
@@ -64,7 +61,7 @@ fn build_man(man_dir: &Path) {
         .spawn()
     {
         Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
-            if env::var("FISH_BUILD_DOCS") == Ok("1".to_string()) {
+            if env_var("FISH_BUILD_DOCS") == Some("1".to_string()) {
                 panic!("Could not find sphinx-build to build man pages.\nInstall sphinx or disable building the docs by setting $FISH_BUILD_DOCS=0.");
             }
             rsconf::warn!("Cannot find sphinx-build to build man pages.");
diff --git a/crates/gettext-maps/build.rs b/crates/gettext-maps/build.rs
index 078cce37d..4e08cf6c9 100644
--- a/crates/gettext-maps/build.rs
+++ b/crates/gettext-maps/build.rs
@@ -1,10 +1,11 @@
 use std::{
-    env,
     ffi::OsStr,
     path::{Path, PathBuf},
     process::{Command, Stdio},
 };
 
+use fish_build_helper::env_var;
+
 fn main() {
     let cache_dir =
         PathBuf::from(fish_build_helper::fish_build_dir()).join("fish-localization-map-cache");
@@ -27,7 +28,7 @@ fn embed_localizations(cache_dir: &Path) {
     std::fs::create_dir_all(cache_dir).unwrap();
 
     let localization_map_path =
-        Path::new(&env::var("OUT_DIR").unwrap()).join("localization_maps.rs");
+        Path::new(&env_var("OUT_DIR").unwrap()).join("localization_maps.rs");
     let mut localization_map_file = BufWriter::new(File::create(&localization_map_path).unwrap());
 
     // This will become a map which maps from language identifiers to maps containing localizations