diff --git a/pkgs/build-support/rust/fetch-cargo-tarball/default.nix b/pkgs/build-support/rust/fetch-cargo-tarball/default.nix
index 075e78a14e1e..adbfe98d8103 100644
--- a/pkgs/build-support/rust/fetch-cargo-tarball/default.nix
+++ b/pkgs/build-support/rust/fetch-cargo-tarball/default.nix
@@ -73,7 +73,7 @@ in stdenv.mkDerivation ({
 
     ${cargoUpdateHook}
 
-    # Override the `http.cainfo` option usually specified in `.cargo/config.toml`.
+    # Override the `http.cainfo` option usually specified in `.cargo/config`.
     export CARGO_HTTP_CAINFO=${cacert}/etc/ssl/certs/ca-bundle.crt
 
     if grep '^source = "git' Cargo.lock; then
@@ -96,7 +96,7 @@ in stdenv.mkDerivation ({
 
     # Packages with git dependencies generate non-default cargo configs, so
     # always install it rather than trying to write a standard default template.
-    install -D $CARGO_CONFIG $name/.cargo/config.toml;
+    install -D $CARGO_CONFIG $name/.cargo/config;
 
     runHook postBuild
   '';
diff --git a/pkgs/build-support/rust/hooks/cargo-setup-hook.sh b/pkgs/build-support/rust/hooks/cargo-setup-hook.sh
index ccb2e565d05c..693c0b08759e 100644
--- a/pkgs/build-support/rust/hooks/cargo-setup-hook.sh
+++ b/pkgs/build-support/rust/hooks/cargo-setup-hook.sh
@@ -22,7 +22,7 @@ cargoSetupPostUnpackHook() {
         mkdir .cargo
     fi
 
-    config="$cargoDepsCopy/.cargo/config.toml";
+    config="$cargoDepsCopy/.cargo/config";
     if [[ ! -e $config ]]; then
       config=@defaultConfig@
     fi;
@@ -30,9 +30,9 @@ cargoSetupPostUnpackHook() {
     tmp_config=$(mktemp)
     substitute $config $tmp_config \
       --subst-var-by vendor "$cargoDepsCopy"
-    cat ${tmp_config} >> .cargo/config.toml
+    cat ${tmp_config} >> .cargo/config
 
-    cat >> .cargo/config.toml <<'EOF'
+    cat >> .cargo/config <<'EOF'
     @cargoConfig@
 EOF
 
diff --git a/pkgs/build-support/rust/import-cargo-lock.nix b/pkgs/build-support/rust/import-cargo-lock.nix
index 0a365ddecba9..e3fe57ef06da 100644
--- a/pkgs/build-support/rust/import-cargo-lock.nix
+++ b/pkgs/build-support/rust/import-cargo-lock.nix
@@ -226,7 +226,7 @@ let
       else "cp $lockFileContentsPath $out/Cargo.lock"
     }
 
-    cat > $out/.cargo/config.toml <<EOF
+    cat > $out/.cargo/config <<EOF
 [source.crates-io]
 replace-with = "vendored-sources"
 
@@ -237,7 +237,7 @@ EOF
     declare -A keysSeen
 
     for registry in ${toString (builtins.attrNames extraRegistries)}; do
-      cat >> $out/.cargo/config.toml <<EOF
+      cat >> $out/.cargo/config <<EOF
 
 [source."$registry"]
 registry = "$registry"
@@ -253,7 +253,7 @@ EOF
         key=$(sed 's/\[source\."\(.*\)"\]/\1/; t; d' < "$crate/.cargo-config")
         if [[ -z ''${keysSeen[$key]} ]]; then
           keysSeen[$key]=1
-          cat "$crate/.cargo-config" >> $out/.cargo/config.toml
+          cat "$crate/.cargo-config" >> $out/.cargo/config
         fi
       fi
     done
diff --git a/pkgs/development/compilers/rust/rustc.nix b/pkgs/development/compilers/rust/rustc.nix
index abb887787b77..1a7e22363acb 100644
--- a/pkgs/development/compilers/rust/rustc.nix
+++ b/pkgs/development/compilers/rust/rustc.nix
@@ -215,7 +215,7 @@ in stdenv.mkDerivation (finalAttrs: {
     export JEMALLOC_SYS_WITH_LG_VADDR=48
   '' + lib.optionalString (!(finalAttrs.src.passthru.isReleaseTarball or false)) ''
     mkdir .cargo
-    cat > .cargo/config.toml <<\EOF
+    cat > .cargo/config <<\EOF
     [source.crates-io]
     replace-with = "vendored-sources"
     [source.vendored-sources]
diff --git a/pkgs/development/ruby-modules/gem-config/default.nix b/pkgs/development/ruby-modules/gem-config/default.nix
index 3e1453d8154d..2e59b8a99cc1 100644
--- a/pkgs/development/ruby-modules/gem-config/default.nix
+++ b/pkgs/development/ruby-modules/gem-config/default.nix
@@ -326,7 +326,7 @@ in
       rustc.unwrapped
     ];
     preBuild = ''
-      cat ../.cargo/config.toml > ext/fast_mmaped_file_rs/.cargo/config.toml
+      cat ../.cargo/config > ext/fast_mmaped_file_rs/.cargo/config.toml
       sed -i "s|cargo-vendor-dir|$PWD/../cargo-vendor-dir|" ext/fast_mmaped_file_rs/.cargo/config.toml
     '';
     postInstall = ''