diff --git a/src/lib.rs b/src/lib.rs
index 7a82cfa..4454381 100755
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -204,7 +204,19 @@ fn wait_for_other_builds( build_dir: &Path ) {
         thread::sleep( Duration::from_secs(5) );
         waiting = false;
         for entry in WalkDir::new( build_dir ) {
-            let entry = entry.unwrap();
+            // Sibling crates' build scripts can create and delete tempfiles
+            // inside this directory while we're walking. WalkDir surfaces
+            // those as Err(NotFound) at iteration time. Don't panic — the
+            // directory is still in flux, so just keep waiting another
+            // round. A NotFound here means we definitely shouldn't declare
+            // the build "stable" yet.
+            let entry = match entry {
+                Ok( e ) => e,
+                Err( _ ) => {
+                    waiting = true;
+                    continue;
+                }
+            };
             let path = entry.path();
             if generated.insert( path.to_owned() ) {
                 waiting = true;
@@ -231,15 +243,17 @@ fn locate_manifest_paths() -> HashMap<PathBuf,Vec<String>> {
                 let path = entry.path();
                 if path.is_dir() {
                     let inwelling_file_path = path.join("out").join( MANIFEST_DIR_INWELLING );
-                    if inwelling_file_path.exists() {
-                        let contents = fs::read_to_string( &inwelling_file_path )
-                            .expect( &format!( "to read {:?} to get one manifest path", inwelling_file_path ));
+                    // The .exists() check and the subsequent read are not
+                    // atomic — sibling builds can clean up the file between
+                    // them. Use match-on-read instead of expect so a TOCTOU
+                    // race becomes a graceful skip instead of a panic.
+                    if let Ok( contents ) = fs::read_to_string( &inwelling_file_path ) {
                         let mut lines = contents.lines();
-                        let manifest_dir = lines.next()
-                            .expect( &format!( "{:?} should contain the line of manifest dir.", inwelling_file_path ));
-                        path_bufs
-                            .entry( PathBuf::from( manifest_dir ).join( "Cargo.toml" ))
-                            .or_insert_with( || lines.map( ToOwned::to_owned ).collect() );
+                        if let Some( manifest_dir ) = lines.next() {
+                            path_bufs
+                                .entry( PathBuf::from( manifest_dir ).join( "Cargo.toml" ))
+                                .or_insert_with( || lines.map( ToOwned::to_owned ).collect() );
+                        }
     }}}}}
     path_bufs
 }