--- file_not_specified_in_diff	
+++ file_not_specified_in_diff	
@@ -, +, @@ 
- x86_64-unknown-linux-musl, and
- x86-64-gentoo-linux-musl
-gentoo- as a vendor target, but
-unknown-.
-gentoo- and tries to use it, without
-gentoo- installed as a Rust target.
--- a/build/moz.configure/rust.configure
+++ b/build/moz.configure/rust.configure
@@ -275,6 +275,7 @@ def rust_supported_targets(rustc):
     return data
 
 
+@imports('os')
 def detect_rustc_target(
     host_or_target, compiler_info, arm_target, rust_supported_targets
 ):
@@ -396,7 +397,7 @@ def detect_rustc_target(
 
         return None
 
-    rustc_target = find_candidate(candidates)
+    rustc_target = os.environ.get('RUST_TARGET', find_candidate(candidates))
 
     if rustc_target is None:
         die("Don't know how to translate {} for rustc".format(host_or_target.alias))