--- a/.cargo/config.in
+++ b/.cargo/config.in
@@ -1,8 +1,13 @@
+# Note: if you add more configure substitutions here with required values
+# you will also need to fix the sed commands in:
+# taskcluster/scripts/builder/build-sm-mozjs-crate.sh
+# taskcluster/scripts/builder/build-sm-rust-bindings.sh
+
 [source.crates-io]
 registry = 'https://github.com/rust-lang/crates.io-index'
 replace-with = 'vendored-sources'
 
 [source."https://github.com/gankro/serde"]
 git = "https://github.com/gankro/serde"
 branch = "deserialize_from_enums3"
 replace-with = "vendored-sources"

--- a/taskcluster/scripts/builder/build-sm-mozjs-crate.sh
+++ b/taskcluster/scripts/builder/build-sm-mozjs-crate.sh
@@ -2,17 +2,17 @@
 
 set -xe
 
 source $(dirname $0)/sm-tooltool-config.sh
 
 # Ensure that we have a .config/cargo that points us to our vendored crates
 # rather than to crates.io.
 cd "$SRCDIR/.cargo"
-sed -e "s|@top_srcdir@|$SRCDIR|" < config.in | tee config
+sed -e "s|@top_srcdir@|$SRCDIR|" -e 's|@[^@]*@||g' < config.in > config
 
 cd "$SRCDIR/js/src"
 
 export PATH="$PATH:$TOOLTOOL_CHECKOUT/cargo/bin:$TOOLTOOL_CHECKOUT/rustc/bin"
 export RUST_BACKTRACE=1
 
 cargo build --verbose --frozen --features debugmozjs
 cargo build --verbose --frozen

--- a/taskcluster/scripts/builder/build-sm-rust-bindings.sh
+++ b/taskcluster/scripts/builder/build-sm-rust-bindings.sh
@@ -2,17 +2,17 @@
 
 set -xe
 
 source $(dirname $0)/sm-tooltool-config.sh
 
 # Ensure that we have a .config/cargo that points us to our vendored crates
 # rather than to crates.io.
 cd "$SRCDIR/.cargo"
-sed -e "s|@top_srcdir@|$SRCDIR|" < config.in | tee config
+sed -e "s|@top_srcdir@|$SRCDIR|" -e 's|@[^@]*@||g' < config.in > config
 
 cd "$SRCDIR/js/rust"
 
 # Enable backtraces if we panic.
 export RUST_BACKTRACE=1
 
 cargo test --verbose --frozen --features debugmozjs
 cargo test --verbose --frozen