diff --git a/ofborg/src/outpathdiff.rs b/ofborg/src/outpathdiff.rs
index 46dde02..feab9a4 100644
--- a/ofborg/src/outpathdiff.rs
+++ b/ofborg/src/outpathdiff.rs
@@ -11,8 +11,7 @@ use ofborg::nix;
 use std::io::Write;
 
 pub struct OutPathDiff {
-    path: PathBuf,
-    nix: nix::Nix,
+    calculator: OutPaths,
     pub original: Option<HashMap<String, String>>,
     pub current: Option<HashMap<String, String>>,
 }
@@ -20,8 +19,7 @@ pub struct OutPathDiff {
 impl OutPathDiff {
     pub fn new(nix: nix::Nix, path: PathBuf) -> OutPathDiff {
         OutPathDiff {
-            nix: nix,
-            path: path,
+            calculator: OutPaths::new(nix, path, false),
             original: None,
             current: None,
         }
@@ -106,6 +104,30 @@ impl OutPathDiff {
         return None;
     }
 
+    fn run(&mut self) -> Result<File, File> {
+        self.calculator.find()
+    }
+}
+
+pub struct OutPaths {
+    path: PathBuf,
+    nix: nix::Nix,
+    check_meta: bool,
+}
+
+impl OutPaths    {
+    pub fn new(nix: nix::Nix, path: PathBuf, check_meta: bool) -> OutPaths    {
+        OutPaths {
+            nix: nix,
+            path: path,
+            check_meta: check_meta,
+        }
+    }
+
+    pub fn find(&self) -> Result<File, File> {
+        self.run()
+    }
+
     fn run(&self) -> Result<File, File> {
         self.place_nix();
         let ret = self.execute();
@@ -115,31 +137,40 @@ impl OutPathDiff {
 
     fn place_nix(&self) {
         let mut file = File::create(self.nix_path()).expect("Failed to create nix out path check");
-        file.write_all(include_str!("rebuild-amount.nix").as_bytes()).expect("");
+        file.write_all(include_str!("outpaths.nix").as_bytes()).expect("Failed to place outpaths.nix");
     }
 
     fn remove_nix(&self) {
-        fs::remove_file(self.nix_path()).expect(":)");
+        fs::remove_file(self.nix_path()).expect("Failed to delete outpaths.nix");
     }
 
     fn nix_path(&self) -> PathBuf {
         let mut dest = self.path.clone();
-        dest.push(".gc-of-borg-out-list.nix");
+        dest.push(".gc-of-borg-outpaths.nix");
 
         dest
     }
 
-    fn execute(&self) -> Result<File, File>{
+    fn execute(&self) -> Result<File, File> {
+        let check_meta: String;
+
+        if self.check_meta {
+            check_meta = String::from("true");
+        } else {
+            check_meta = String::from("false");
+        }
+
         self.nix.safely(
             "nix-env",
             &self.path,
             vec![
                 String::from("-f"),
-                String::from(".gc-of-borg-out-list.nix"),
+                String::from(".gc-of-borg-outpaths.nix"),
                 String::from("-qaP"),
                 String::from("--no-name"),
                 String::from("--out-path"),
                 String::from("--show-trace"),
+                String::from("--arg"), String::from("checkMeta"), check_meta,
             ],
             true
         )
diff --git a/ofborg/src/rebuild-amount.nix b/ofborg/src/outpaths.nix
similarity index 77%
rename from ofborg/src/rebuild-amount.nix
rename to ofborg/src/outpaths.nix
index f3ffe95..7f44db3 100644
--- a/ofborg/src/rebuild-amount.nix
+++ b/ofborg/src/outpaths.nix
@@ -1,8 +1,19 @@
+{ checkMeta ? false }:
 let
   lib = import ./lib;
   hydraJobs = import ./pkgs/top-level/release.nix
     # Compromise: accuracy vs. resources needed for evaluation.
-    { supportedSystems = [ "x86_64-linux" "x86_64-darwin" ]; };
+    {
+      supportedSystems = [ "x86_64-linux" "x86_64-darwin" ];
+      nixpkgsArgs = {
+        config = {
+          allowBroken = true;
+          allowUnfree = true;
+          inHydra = true;
+          checkMeta = checkMeta;
+        };
+      };
+    };
   recurseIntoAttrs = attrs: attrs // { recurseForDerivations = true; };
 
   # hydraJobs leaves recurseForDerivations as empty attrmaps;
diff --git a/ofborg/src/tasks/massrebuilder.rs b/ofborg/src/tasks/massrebuilder.rs
index bb5376d..904a111 100644
--- a/ofborg/src/tasks/massrebuilder.rs
+++ b/ofborg/src/tasks/massrebuilder.rs
@@ -14,7 +14,7 @@ use ofborg::nix::Nix;
 
 use ofborg::worker;
 use ofborg::tagger::{StdenvTagger,RebuildTagger};
-use ofborg::outpathdiff::OutPathDiff;
+use ofborg::outpathdiff::{OutPaths, OutPathDiff};
 use ofborg::evalchecker::EvalChecker;
 use ofborg::commitstatus::CommitStatus;
 use amqp::protocol::basic::{Deliver,BasicProperties};
@@ -262,7 +262,7 @@ impl worker::SimpleWorker for MassRebuildWorker {
             ),
         ];
 
-        let eval_results: bool = eval_checks.into_iter()
+        let mut eval_results: bool = eval_checks.into_iter()
             .map(|check|
                  {
                      let mut status = CommitStatus::new(
@@ -306,6 +306,46 @@ impl worker::SimpleWorker for MassRebuildWorker {
             )
             .all(|status| status == Ok(()));
 
+        if eval_results {
+            let mut status = CommitStatus::new(
+                repo.statuses(),
+                job.pr.head_sha.clone(),
+                String::from("Meta Field Checks"),
+                String::from("config.nix: checkMeta = true"),
+                None
+            );
+
+            status.set(hubcaps::statuses::State::Pending);
+
+            let state: hubcaps::statuses::State;
+            let gist_url: Option<String>;
+
+            let checker = OutPaths::new(
+                self.nix.clone(),
+                PathBuf::from(&refpath),
+                true
+            );
+            match checker.find() {
+                Ok(_) => {
+                    state = hubcaps::statuses::State::Success;
+                    gist_url = None;
+                }
+                Err(mut out) => {
+                    eval_results = false;
+                    state = hubcaps::statuses::State::Failure;
+                    gist_url = make_gist(
+                        &gists,
+                        String::from("Meta Check"),
+                        Some(format!("{:?}", state)),
+                        file_to_str(&mut out),
+                    );
+                }
+            }
+
+            status.set_url(gist_url);
+            status.set(state.clone());
+        }
+
         if eval_results {
             overall_status.set_with_description(
                 "Calculating Changed Outputs",