diff --git a/src/internal/partial_solution.rs b/src/internal/partial_solution.rs
index 1b683b9d..c2d88bed 100644
--- a/src/internal/partial_solution.rs
+++ b/src/internal/partial_solution.rs
@@ -141,7 +141,13 @@ impl<P: Package, VS: VersionSet> PartialSolution<P, VS> {
                     AssignmentsIntersection::Decision(_) => panic!("Already existing decision"),
                     // Cannot be called if the versions is not contained in the terms intersection.
                     AssignmentsIntersection::Derivations(term) => {
-                        debug_assert!(term.contains(&version))
+                        debug_assert!(
+                            term.contains(&version),
+                            "{}: {} was expected to be contained in {}",
+                            package,
+                            version,
+                            term,
+                        )
                     }
                 },
             }