diff --git a/.travis.yml b/.travis.yml
index 45d6696..694c088 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,7 +1,9 @@
 language: nix
 matrix:
   include:
-  - script:
-    - nix-shell --run checkPhase
-    - nix-shell --run checkPhase --arg useNix1 true
-    - nix-build -A ofborg.rs
+    - name: checkPhase - Nix 2
+      script: nix-shell --run checkPhase --arg useNix1 false
+    - name: checkPhase - Nix 1
+      script: nix-shell --run checkPhase --arg useNix1 true
+    - name: nix-build
+      script: nix-build -A ofborg.rs
diff --git a/default.nix b/default.nix
index e499969..eefd8e7 100644
--- a/default.nix
+++ b/default.nix
@@ -23,9 +23,6 @@ in {
   in pkgs.runCommand "ofborg-rs-symlink-compat" {
     src = stripDeps build;
   } ''
-
-    set -x
-
     mkdir -p $out/bin
     for f in $(find $src -type f); do
       bn=$(basename "$f")
@@ -43,6 +40,32 @@ in {
     test -e $out/bin/github_comment_poster
     test -e $out/bin/log_message_collector
     test -e $out/bin/evaluation_filter
+
+    # Verify that the outpath contains the version number matching the
+    # Cargo.toml
+    if ! grep -q 'version = "${drv.crateVersion}"' ${./ofborg/Cargo.toml}; then
+      cat <<EOF
+
+
+
+
+
+Build failed because you bumped the Cargo
+version without regenerating the carnix
+file.
+
+Run:
+
+
+
+    nix-shell --run ./nix/update-carnix.sh
+
+
+and commit those changes.
+
+
+EOF
+    fi
   '';
 
   ofborg.php = pkgs.runCommand
diff --git a/nix/ofborg-carnix.nix b/nix/ofborg-carnix.nix
index 5875ff2..74bc4d8 100644
--- a/nix/ofborg-carnix.nix
+++ b/nix/ofborg-carnix.nix
@@ -45,7 +45,7 @@ let kernel = buildPlatform.parsed.kernel.name;
     ) [] (builtins.attrNames feat);
 in
 rec {
-  ofborg = f: ofborg_0_1_6 { features = ofborg_0_1_6_features { ofborg_0_1_6 = f; }; };
+  ofborg = f: ofborg_0_1_7 { features = ofborg_0_1_7_features { ofborg_0_1_7 = f; }; };
   aho_corasick_0_5_3_ = { dependencies?[], buildDependencies?[], features?[] }: buildRustCrate {
     crateName = "aho-corasick";
     version = "0.5.3";
@@ -427,9 +427,9 @@ rec {
     sha256 = "1y6qnd9r8ga6y8mvlabdrr73nc8cshjjlzbvnanzyj9b8zzkfwk2";
     inherit dependencies buildDependencies features;
   };
-  ofborg_0_1_6_ = { dependencies?[], buildDependencies?[], features?[] }: buildRustCrate {
+  ofborg_0_1_7_ = { dependencies?[], buildDependencies?[], features?[] }: buildRustCrate {
     crateName = "ofborg";
-    version = "0.1.6";
+    version = "0.1.7";
     authors = [ "Graham Christensen <graham@grahamc.com>" ];
     src = include [ "Cargo.toml" "Cargo.lock" "src" "test-srcs" "build.rs" ] ./../ofborg;
     build = "build.rs";
@@ -1449,10 +1449,10 @@ rec {
     libc_0_2_40.default = true;
     num_cpus_1_8_0.default = (f.num_cpus_1_8_0.default or true);
   }) [ libc_0_2_40_features ];
-  ofborg_0_1_6 = { features?(ofborg_0_1_6_features {}) }: ofborg_0_1_6_ {
+  ofborg_0_1_7 = { features?(ofborg_0_1_7_features {}) }: ofborg_0_1_7_ {
     dependencies = mapFeatures features ([ amqp_0_1_0 either_1_5_0 env_logger_0_4_3 fs2_0_4_3 hubcaps_0_3_16 hyper_0_10_13 hyper_native_tls_0_2_4 log_0_3_8 lru_cache_0_1_1 md5_0_3_7 nom_4_0_0_beta3 serde_1_0_43 serde_derive_1_0_43 serde_json_1_0_16 sys_info_0_5_6 tempfile_2_2_0 uuid_0_4_0 ]);
   };
-  ofborg_0_1_6_features = f: updateFeatures f (rec {
+  ofborg_0_1_7_features = f: updateFeatures f (rec {
     amqp_0_1_0.default = true;
     either_1_5_0.default = true;
     env_logger_0_4_3.default = true;
@@ -1464,7 +1464,7 @@ rec {
     lru_cache_0_1_1.default = true;
     md5_0_3_7.default = true;
     nom_4_0_0_beta3.default = true;
-    ofborg_0_1_6.default = (f.ofborg_0_1_6.default or true);
+    ofborg_0_1_7.default = (f.ofborg_0_1_7.default or true);
     serde_1_0_43.default = true;
     serde_derive_1_0_43.default = true;
     serde_json_1_0_16.default = true;
diff --git a/nix/update-carnix.sh b/nix/update-carnix.sh
index d46e546..a711c01 100755
--- a/nix/update-carnix.sh
+++ b/nix/update-carnix.sh
@@ -1,11 +1,18 @@
 #!/bin/sh
 
+set -eu
+
 cd nix
 
 patched_carnix() {
     src=$1
     result=$2
 
+    (
+        cd "$(dirname "$src")"
+        cargo build
+    )
+
     carnix "$src"  --output "$result"
     patch -p1 "$result" ./carnix.patch
 }
diff --git a/ofborg/Cargo.lock b/ofborg/Cargo.lock
index 1d4f51a..e4a4263 100644
--- a/ofborg/Cargo.lock
+++ b/ofborg/Cargo.lock
@@ -395,7 +395,7 @@ dependencies = [
 
 [[package]]
 name = "ofborg"
-version = "0.1.6"
+version = "0.1.7"
 dependencies = [
  "amqp 0.1.0 (git+https://github.com/grahamc/rust-amqp.git)",
  "either 1.5.0 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/ofborg/Cargo.toml b/ofborg/Cargo.toml
index 336292a..f69479a 100644
--- a/ofborg/Cargo.toml
+++ b/ofborg/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ofborg"
-version = "0.1.6"
+version = "0.1.7"
 authors = ["Graham Christensen <graham@grahamc.com>"]
 include = ["Cargo.toml", "Cargo.lock", "src", "test-srcs", "build.rs"]
 build = "build.rs"
diff --git a/ofborg/src/tasks/log_message_collector.rs b/ofborg/src/tasks/log_message_collector.rs
index 47ad006..e63a595 100644
--- a/ofborg/src/tasks/log_message_collector.rs
+++ b/ofborg/src/tasks/log_message_collector.rs
@@ -9,7 +9,7 @@ use std::io::Write;
 
 use ofborg::writetoline::LineWriter;
 use ofborg::message::buildlogmsg::{BuildLogStart, BuildLogMsg};
-use ofborg::message::buildresult::{BuildStatus, BuildResult};
+use ofborg::message::buildresult::BuildResult;
 use ofborg::worker;
 use amqp::protocol::basic::{Deliver, BasicProperties};
 
@@ -248,6 +248,7 @@ mod tests {
     use std::path::PathBuf;
     use ofborg::worker::SimpleWorker;
     use ofborg::test_scratch::TestScratch;
+    use ofborg::message::buildresult::BuildStatus;
     use ofborg::message::{Pr,Repo};
 
     fn make_worker(path: PathBuf) -> LogMessageCollector {
@@ -455,18 +456,18 @@ mod tests {
             );
         }
 
-        let mut pr = p.path();
-        let mut s = String::new();
-        pr.push("routing-key-foo/attempt-id-foo.metadata.json");
-        File::open(pr).unwrap().read_to_string(&mut s).unwrap();
-        assert_eq!(&s, "{\"system\":\"foobar-x8664\",\"identity\":\"my-identity\",\"attempt_id\":\"my-attempt-id\",\"attempted_attrs\":[\"foo\"],\"skipped_attrs\":[\"bar\"]}");
+        let mut prm = p.path();
+        let mut sm = String::new();
+        prm.push("routing-key-foo/attempt-id-foo.metadata.json");
+        File::open(prm).unwrap().read_to_string(&mut sm).unwrap();
+        assert_eq!(&sm, "{\"system\":\"foobar-x8664\",\"identity\":\"my-identity\",\"attempt_id\":\"my-attempt-id\",\"attempted_attrs\":[\"foo\"],\"skipped_attrs\":[\"bar\"]}");
 
 
-        let mut pr = p.path();
-        let mut s = String::new();
-        pr.push("routing-key-foo/attempt-id-foo");
-        File::open(pr).unwrap().read_to_string(&mut s).unwrap();
-        assert_eq!(&s, "line-1\n\n\n\nline-5\n");
+        let mut prf = p.path();
+        let mut sf = String::new();
+        prf.push("routing-key-foo/attempt-id-foo");
+        File::open(prf).unwrap().read_to_string(&mut sf).unwrap();
+        assert_eq!(&sf, "line-1\n\n\n\nline-5\n");
 
 
         let mut pr = p.path();
@@ -475,10 +476,10 @@ mod tests {
         File::open(pr).unwrap().read_to_string(&mut s).unwrap();
         assert_eq!(&s, "\n\nline-3\n");
 
-        let mut pr = p.path();
-        let mut s = String::new();
-        pr.push("routing-key-foo/attempt-id-foo.result.json");
-        File::open(pr).unwrap().read_to_string(&mut s).unwrap();
-        assert_eq!(&s, "{\"repo\":{\"owner\":\"NixOS\",\"name\":\"ofborg\",\"full_name\":\"NixOS/ofborg\",\"clone_url\":\"https://github.com/nixos/ofborg.git\"},\"pr\":{\"target_branch\":\"scratch\",\"number\":42,\"head_sha\":\"6dd9f0265d52b946dd13daf996f30b64e4edb446\"},\"system\":\"x86_64-linux\",\"output\":[],\"attempt_id\":\"attempt-id-foo\",\"request_id\":\"bogus-request-id\",\"success\":true,\"status\":\"Success\",\"skipped_attrs\":[\"bar\"],\"attempted_attrs\":[\"foo\"]}");
+        let mut prr = p.path();
+        let mut sr = String::new();
+        prr.push("routing-key-foo/attempt-id-foo.result.json");
+        File::open(prr).unwrap().read_to_string(&mut sr).unwrap();
+        assert_eq!(&sr, "{\"repo\":{\"owner\":\"NixOS\",\"name\":\"ofborg\",\"full_name\":\"NixOS/ofborg\",\"clone_url\":\"https://github.com/nixos/ofborg.git\"},\"pr\":{\"target_branch\":\"scratch\",\"number\":42,\"head_sha\":\"6dd9f0265d52b946dd13daf996f30b64e4edb446\"},\"system\":\"x86_64-linux\",\"output\":[],\"attempt_id\":\"attempt-id-foo\",\"request_id\":\"bogus-request-id\",\"success\":true,\"status\":\"Success\",\"skipped_attrs\":[\"bar\"],\"attempted_attrs\":[\"foo\"]}");
     }
 }
diff --git a/ofborg/src/test_scratch.rs b/ofborg/src/test_scratch.rs
index cec800b..1904ee0 100644
--- a/ofborg/src/test_scratch.rs
+++ b/ofborg/src/test_scratch.rs
@@ -8,27 +8,34 @@ pub struct TestScratch {
 
 impl TestScratch {
     pub fn new_dir(ident: &str) -> TestScratch {
-        let path = TestScratch {
+        let scratch = TestScratch {
             root: Path::new(env!("CARGO_MANIFEST_DIR"))
                 .join("test-scratch")
                 .join("dirs")
                 .join(&format!("dir-{}", ident)),
         };
-        fs::create_dir_all(path.root.parent().unwrap()).unwrap();
 
-        return path;
+        TestScratch::create_dir(&scratch);
+
+        return scratch;
     }
 
     pub fn new_file(ident: &str) -> TestScratch {
-        let path = TestScratch {
+        let scratch = TestScratch {
             root: Path::new(env!("CARGO_MANIFEST_DIR"))
                 .join("test-scratch")
                 .join("files")
                 .join(&format!("file-{}", ident)),
         };
-        fs::create_dir_all(path.root.parent().unwrap()).unwrap();
 
-        return path;
+        TestScratch::create_dir(&scratch);
+        return scratch;
+    }
+
+    fn create_dir(path: &TestScratch) {
+        let target = path.root.parent().unwrap();
+        debug!("Creating directory {:?}", target);
+        fs::create_dir_all(target).unwrap();
     }
 
     pub fn path(&self) -> PathBuf {
@@ -42,6 +49,7 @@ impl TestScratch {
 
 impl Drop for TestScratch {
     fn drop(&mut self) {
+        debug!("Deleting root {:?}", self.root);
         Command::new("rm")
             .arg("-rf")
             .arg(self.root.clone())
diff --git a/ofborg/test-srcs/build-pr/default.nix b/ofborg/test-srcs/build-pr/default.nix
index 6c8596c..35e2ada 100644
--- a/ofborg/test-srcs/build-pr/default.nix
+++ b/ofborg/test-srcs/build-pr/default.nix
@@ -4,7 +4,7 @@ in {
   success = derivation {
     name = "success";
     system = builtins.currentSystem;
-    builder = nix.shell;
+    builder = builtins.storePath nix.shell;
     args = [
       "-c"
       "echo hi; printf '1\n2\n3\n4\n'; echo ${toString builtins.currentTime} > $out" ];
@@ -13,7 +13,7 @@ in {
   failed = derivation {
     name = "failed";
     system = builtins.currentSystem;
-    builder = nix.shell;
+    builder = builtins.storePath nix.shell;
     args = [
       "-c"
       "echo hi; echo ${toString builtins.currentTime}" ];
diff --git a/ofborg/test-srcs/build/default.nix b/ofborg/test-srcs/build/default.nix
index 840aa12..ba7eb25 100644
--- a/ofborg/test-srcs/build/default.nix
+++ b/ofborg/test-srcs/build/default.nix
@@ -4,7 +4,7 @@ in {
   success = derivation {
     name = "success";
     system = builtins.currentSystem;
-    builder = nix.shell;
+    builder = builtins.storePath nix.shell;
     args = [
       "-c"
       "echo hi; echo ${toString builtins.currentTime} > $out" ];
@@ -13,7 +13,7 @@ in {
   failed = derivation {
     name = "failed";
     system = builtins.currentSystem;
-    builder = nix.shell;
+    builder = builtins.storePath nix.shell;
     args = [
       "-c"
       "echo hi; echo ${toString builtins.currentTime}" ];
diff --git a/ofborg/test-srcs/eval-mixed-failure/default.nix b/ofborg/test-srcs/eval-mixed-failure/default.nix
index 8d157ac..a4f5290 100644
--- a/ofborg/test-srcs/eval-mixed-failure/default.nix
+++ b/ofborg/test-srcs/eval-mixed-failure/default.nix
@@ -4,7 +4,7 @@ in rec {
   success = derivation {
     name = "success";
     system = builtins.currentSystem;
-    builder = nix.shell;
+    builder = builtins.storePath nix.shell;
     args = [
       "-c"
       "echo hi; echo ${toString builtins.currentTime} > $out" ];
@@ -13,7 +13,7 @@ in rec {
   failed = derivation {
     name = "failed";
     system = builtins.currentSystem;
-    builder = nix.shell;
+    builder = builtins.storePath nix.shell;
     args = [
       "-c"
       "echo hi; echo ${toString builtins.currentTime}; echo ${success}" ];
@@ -22,7 +22,7 @@ in rec {
   passes-instantiation = derivation {
     name = "passes-instantiation";
     system = builtins.currentSystem;
-    builder = nix.shell;
+    builder = builtins.storePath nix.shell;
     args = [
       "-c"
       "echo this ones cool" ];
diff --git a/ofborg/test-srcs/eval/default.nix b/ofborg/test-srcs/eval/default.nix
index 35981f7..34a7247 100644
--- a/ofborg/test-srcs/eval/default.nix
+++ b/ofborg/test-srcs/eval/default.nix
@@ -4,7 +4,7 @@ in rec {
   success = derivation {
     name = "success";
     system = builtins.currentSystem;
-    builder = nix.shell;
+    builder = builtins.storePath nix.shell;
     args = [
       "-c"
       "echo hi; echo ${toString builtins.currentTime} > $out" ];
@@ -13,7 +13,7 @@ in rec {
   failed = derivation {
     name = "failed";
     system = builtins.currentSystem;
-    builder = nix.shell;
+    builder = builtins.storePath nix.shell;
     args = [
       "-c"
       "echo hi; echo ${toString builtins.currentTime}; echo ${success}" ];