diff --git a/lib/spack/spack/solver/asp.py b/lib/spack/spack/solver/asp.py
index cd095de51ef..fd01fa5c655 100644
--- a/lib/spack/spack/solver/asp.py
+++ b/lib/spack/spack/solver/asp.py
@@ -572,7 +572,7 @@ def format_unsolved(unsolved_specs):
         for input_spec, candidate in unsolved_specs:
             msg += f"\n\tInput spec: {str(input_spec)}"
             if candidate:
-                msg += f"\n\tCandidate spec: {str(candidate)}"
+                msg += f"\n\tCandidate spec: {candidate.long_spec}"
             else:
                 msg += "\n\t(No candidate specs from solver)"
         return msg