foo.diff

diff --git a/src/cargo/ops/cargo_rustc/custom_build.rs b/src/cargo/ops/cargo_rustc/custom_build.rs
index 727f0d3..d2c34b9 100644
--- a/src/cargo/ops/cargo_rustc/custom_build.rs
+++ b/src/cargo/ops/cargo_rustc/custom_build.rs
@@ -316,15 +316,10 @@ impl BuildState {
     }
 
     fn has_override(&self, unit: &Unit) -> bool {
-        let key = unit.pkg.manifest().links().map(|l| (l.to_string(), unit.kind));
-        match key.and_then(|k| self.overrides.get(&k)) {
-            Some(output) => {
-                self.insert(unit.pkg.package_id().clone(), unit.kind,
-                            output.clone());
-                true
-            }
-            None => false,
-        }
+        self.outputs
+            .lock()
+            .unwrap()
+            .contains_key(&(unit.pkg.package_id().clone(), unit.kind))
     }
 }
 
@@ -483,7 +478,7 @@ pub fn build_map<'b, 'cfg>(cx: &mut Context<'b, 'cfg>,
     // Recursive function to build up the map we're constructing. This function
     // memoizes all of its return values as it goes along.
     fn build<'a, 'b, 'cfg>(out: &'a mut HashMap<Unit<'b>, BuildScripts>,
-                           cx: &Context<'b, 'cfg>,
+                           cx: &mut Context<'b, 'cfg>,
                            unit: &Unit<'b>)
                            -> CargoResult<&'a BuildScripts> {
         // Do a quick pre-flight check to see if we've already calculated the
@@ -492,6 +487,15 @@ pub fn build_map<'b, 'cfg>(cx: &mut Context<'b, 'cfg>,
             return Ok(&out[unit])
         }
 
+        let key = unit.pkg.manifest().links().map(|l| (l.to_string(), unit.kind));
+        if let Some(output) = key.and_then(|k| cx.build_state.overrides.get(&k)) {
+            cx.build_state
+                .outputs
+                .lock()
+                .unwrap()
+                .insert((unit.pkg.package_id().clone(), unit.kind), output.clone());
+        }
+
         let mut ret = BuildScripts::default();
 
         if !unit.target.is_custom_build() && unit.pkg.has_custom_build() {