diff --git a/ofborg/src/outpathdiff.rs b/ofborg/src/outpathdiff.rs
index 7b4351f..b5f02ec 100644
--- a/ofborg/src/outpathdiff.rs
+++ b/ofborg/src/outpathdiff.rs
@@ -12,8 +12,8 @@ use std::io::Write;
 
 pub struct OutPathDiff {
     calculator: OutPaths,
-    pub original: Option<HashMap<String, String>>,
-    pub current: Option<HashMap<String, String>>,
+    pub original: Option<PackageOutPaths>,
+    pub current: Option<PackageOutPaths>,
 }
 
 impl OutPathDiff {
@@ -25,36 +25,11 @@ impl OutPathDiff {
         }
     }
 
-    fn parse(&self, f: File) -> HashMap<String, String> {
-        let mut result: HashMap<String, String>;
-        result = HashMap::new();
-
-        {
-            BufReader::new(f)
-                .lines()
-                .filter_map(|line| match line {
-                    Ok(line) => Some(line),
-                    Err(_) => None,
-                })
-                .map(|x| {
-                    let split: Vec<&str> = x.split_whitespace().collect();
-                    if split.len() == 2 {
-                        result.insert(String::from(split[0]), String::from(split[1]));
-                    } else {
-                        info!("Warning: not 2 word segments in {:?}", split);
-                    }
-                })
-                .count();
-        }
-
-        return result;
-    }
-
     pub fn find_before(&mut self) -> Result<bool, File> {
         let x = self.run();
         match x {
             Ok(f) => {
-                self.original = Some(self.parse(f));
+                self.original = Some(f);
                 return Ok(true);
             }
             Err(e) => {
@@ -73,7 +48,7 @@ impl OutPathDiff {
         let x = self.run();
         match x {
             Ok(f) => {
-                self.current = Some(self.parse(f));
+                self.current = Some(f);
                 return Ok(true);
             }
             Err(e) => {
@@ -83,13 +58,13 @@ impl OutPathDiff {
         }
     }
 
-    pub fn calculate_rebuild(self) -> Option<Vec<String>> {
-        let mut rebuild: Vec<String> = vec![];
+    pub fn calculate_rebuild(self) -> Option<Vec<PackageArch>> {
+        let mut rebuild: Vec<PackageArch> = vec![];
 
         if let Some(cur) = self.current {
             if let Some(orig) = self.original {
                 for key in cur.keys() {
-                    trace!("Checking out {}", key);
+                    trace!("Checking out {:?}", key);
                     if cur.get(key) != orig.get(key) {
                         trace!("    {:?} != {:?}", cur.get(key), orig.get(key));
                         rebuild.push(key.clone())
@@ -105,11 +80,22 @@ impl OutPathDiff {
         return None;
     }
 
-    fn run(&mut self) -> Result<File, File> {
+    fn run(&mut self) -> Result<PackageOutPaths, File> {
         self.calculator.find()
     }
 }
 
+type PackageOutPaths = HashMap<PackageArch, OutPath>;
+
+#[derive(Debug, PartialEq, Hash, Eq, Clone)]
+pub struct PackageArch {
+    pub package: Package,
+    pub architecture: Architecture,
+}
+type Package = String;
+type Architecture = String;
+type OutPath = String;
+
 pub struct OutPaths {
     path: PathBuf,
     nix: nix::Nix,
@@ -125,15 +111,19 @@ impl OutPaths {
         }
     }
 
-    pub fn find(&self) -> Result<File, File> {
+    pub fn find(&self) -> Result<PackageOutPaths, File> {
         self.run()
     }
 
-    fn run(&self) -> Result<File, File> {
+    fn run(&self) -> Result<PackageOutPaths, File> {
         self.place_nix();
         let ret = self.execute();
         self.remove_nix();
-        return ret;
+
+        match ret {
+            Ok(file) => Ok(parse_lines(&mut BufReader::new(file))),
+            Err(e) => Err(e),
+        }
     }
 
     fn place_nix(&self) {
@@ -179,3 +169,89 @@ impl OutPaths {
         )
     }
 }
+
+
+fn parse_lines(data: &mut BufRead) -> PackageOutPaths {
+    data.lines()
+        .filter_map(|line| match line {
+            Ok(line) => Some(line),
+            Err(_) => None,
+        })
+        .filter_map(|line| {
+            let split: Vec<&str> = line.split_whitespace().collect();
+            if split.len() == 2 {
+                let outpaths = String::from(split[1]);
+
+                let path: Vec<&str> = split[0].rsplitn(2, ".").collect();
+                if path.len() == 2 {
+                    Some((
+                        PackageArch {
+                            package: String::from(path[1]),
+                            architecture: String::from(path[0]),
+                        },
+                        outpaths,
+                    ))
+                } else {
+                    info!("Warning: Didn't detect an architecture for {:?}", path);
+                    None
+                }
+            } else {
+                info!("Warning: not 2 word segments in {:?}", split);
+                None
+            }
+
+        })
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+
+    use super::*;
+    use std::io::Cursor;
+
+    const TEST_LINES: &'static str = "
+kindlegen.x86_64-darwin                                                    /nix/store/sgabv7byhan6b0rjspd3p1bd7yw91f30-kindlegen-2.9
+python27Packages.pyinotify.i686-linux                                      /nix/store/rba0hbq6i4camvhpj9723dvs4b511ryn-python2.7-pyinotify-0.9.6
+pan.i686-linux                                                             /nix/store/6djnw9s2z5iy0c741qa8yk0k2v6bxrra-pan-0.139
+gnome3.evolution_data_server.aarch64-linux                                 /nix/store/fmxf25kyxb62v9arc64fypb2ilxifsh0-evolution-data-server-3.26.3
+";
+
+    #[test]
+    fn test_parse_outputs() {
+        let mut expect: PackageOutPaths = HashMap::new();
+        expect.insert(
+            PackageArch {
+                package: "kindlegen".to_owned(),
+                architecture: "x86_64-darwin".to_owned(),
+            },
+            "/nix/store/sgabv7byhan6b0rjspd3p1bd7yw91f30-kindlegen-2.9".to_owned(),
+        );
+
+        expect.insert(
+            PackageArch {
+                architecture: "aarch64-linux".to_owned(),
+                package: "gnome3.evolution_data_server".to_owned(),
+            },
+            "/nix/store/fmxf25kyxb62v9arc64fypb2ilxifsh0-evolution-data-server-3.26.3".to_owned(),
+        );
+
+        expect.insert(
+            PackageArch {
+                architecture: "i686-linux".to_owned(),
+                package: "python27Packages.pyinotify".to_owned(),
+            },
+            "/nix/store/rba0hbq6i4camvhpj9723dvs4b511ryn-python2.7-pyinotify-0.9.6".to_owned(),
+        );
+
+        expect.insert(
+            PackageArch {
+                architecture: "i686-linux".to_owned(),
+                package: "pan".to_owned(),
+            },
+            "/nix/store/6djnw9s2z5iy0c741qa8yk0k2v6bxrra-pan-0.139".to_owned(),
+        );
+        assert_eq!(parse_lines(&mut Cursor::new(TEST_LINES)), expect);
+    }
+
+}
diff --git a/ofborg/src/tagger.rs b/ofborg/src/tagger.rs
index 490caba..efe5cc6 100644
--- a/ofborg/src/tagger.rs
+++ b/ofborg/src/tagger.rs
@@ -1,4 +1,5 @@
 use ofborg::tasks;
+use ofborg::outpathdiff::PackageArch;
 
 pub struct StdenvTagger {
     possible: Vec<String>,
@@ -85,26 +86,23 @@ impl RebuildTagger {
         return t;
     }
 
-    pub fn parse_attrs(&mut self, attrs: Vec<String>) {
+    pub fn parse_attrs(&mut self, attrs: Vec<PackageArch>) {
         let mut counter_darwin = 0;
         let mut counter_linux = 0;
 
         for attr in attrs {
-            match attr.rsplit(".").next() {
-                Some("x86_64-darwin") => {
+            match attr.architecture.as_ref() {
+                "x86_64-darwin" => {
                     counter_darwin += 1;
                 }
-                Some("x86_64-linux") => {
+                "x86_64-linux" => {
                     counter_linux += 1;
                 }
-                Some("aarch64-linux") => {}
-                Some("i686-linux") => {}
-                Some(arch) => {
+                "aarch64-linux" => {}
+                "i686-linux" => {}
+                arch => {
                     info!("Unknown arch: {:?}", arch);
                 }
-                None => {
-                    info!("Cannot grok attr: {:?}", attr);
-                }
             }
         }