diff --git a/lib/spack/spack/repo.py b/lib/spack/spack/repo.py
index c4aa991b5d9..307654d3284 100644
--- a/lib/spack/spack/repo.py
+++ b/lib/spack/spack/repo.py
@@ -490,7 +490,7 @@ def read(self, stream):
         self.index = spack.tag.TagIndex.from_json(stream, self.repository)
 
     def update(self, pkg_fullname):
-        self.index.update_package(pkg_fullname)
+        self.index.update_package(pkg_fullname.split(".")[-1])
 
     def write(self, stream):
         self.index.to_json(stream)