diff --git a/lib/spack/spack/spec_parser.py b/lib/spack/spack/spec_parser.py
index 751ffb88751..43addb8ddce 100644
--- a/lib/spack/spack/spec_parser.py
+++ b/lib/spack/spack/spec_parser.py
@@ -164,7 +164,7 @@ def tokenize(text: str) -> Iterator[Token]:
         yield token
 
 
-def parseable_tokens(text: str) -> List[Token]:
+def parseable_tokens(text: str) -> Iterator[Token]:
     """Return non-whitespace tokens from the text passed as input
 
     Raises: