diff --git a/mesonbuild/build.py b/mesonbuild/build.py
index a00209ad45a8..221034e9d0bc 100644
--- a/mesonbuild/build.py
+++ b/mesonbuild/build.py
@@ -1346,7 +1346,7 @@ def get_include_dirs(self) -> T.List['IncludeDirs']:
     def add_deps(self, deps):
         deps = listify(deps)
         for dep in deps:
-            if dep in self.added_deps:
+            if isinstance(dep, T.Hashable) and dep in self.added_deps:
                 continue
 
             if isinstance(dep, dependencies.InternalDependency):