diff --git a/mesonbuild/build.py b/mesonbuild/build.py
index bcd1754e6..020c47b58 100644
--- a/mesonbuild/build.py
+++ b/mesonbuild/build.py
@@ -1035,6 +1035,7 @@ This will become a hard error in a future Meson release.''')
                 if dep not in self.external_deps:
                     self.external_deps.append(dep)
                     self.process_sourcelist(dep.get_sources())
+                self.add_deps(dep.ext_deps)
             elif isinstance(dep, BuildTarget):
                 raise InvalidArguments('''Tried to use a build target as a dependency.
 You probably should put it in link_with instead.''')
diff --git a/mesonbuild/dependencies/base.py b/mesonbuild/dependencies/base.py
index af4b13fad..032fe60a6 100644
--- a/mesonbuild/dependencies/base.py
+++ b/mesonbuild/dependencies/base.py
@@ -115,6 +115,7 @@ class Dependency:
         self.raw_link_args = None
         self.sources = []
         self.methods = self._process_method_kw(kwargs)
+        self.ext_deps = []  # type: List[Dependency]
 
     def __repr__(self):
         s = '<{0} {1}: {2}>'