diff --git a/lib/spack/spack/solver/asp.py b/lib/spack/spack/solver/asp.py
index b5bd5b396b4..2742f07cfc8 100644
--- a/lib/spack/spack/solver/asp.py
+++ b/lib/spack/spack/solver/asp.py
@@ -2710,8 +2710,8 @@ def setup(
         if env:
             dev_specs = tuple(
                 spack.spec.Spec(info["spec"]).constrained(
-                    "dev_path="
-                    f'"{spack.util.path.canonicalize_path(info["path"], default_wd=env.path)}"'
+                    'dev_path="%s"'
+                    % spack.util.path.canonicalize_path(info["path"], default_wd=env.path)
                 )
                 for name, info in env.dev_specs.items()
             )