diff --git a/src/poetry/mixology/version_solver.py b/src/poetry/mixology/version_solver.py
index c1e7a4d3bae..4999a35fd9b 100644
--- a/src/poetry/mixology/version_solver.py
+++ b/src/poetry/mixology/version_solver.py
@@ -96,9 +96,10 @@ def __init__(self, root: ProjectPackage, provider: Provider) -> None:
         self._provider = provider
         self._dependency_cache = DependencyCache(provider)
         self._incompatibilities: dict[str, list[Incompatibility]] = {}
-        self._contradicted_incompatibilities: dict[int, set[Incompatibility]] = (
-            collections.defaultdict(set)
-        )
+        self._contradicted_incompatibilities: set[Incompatibility] = set()
+        self._contradicted_incompatibilities_by_level: dict[
+            int, set[Incompatibility]
+        ] = collections.defaultdict(set)
         self._solution = PartialSolution()
 
     @property
@@ -147,10 +148,7 @@ def _propagate(self, package: str) -> None:
             # we can derive stronger assignments sooner and more eagerly find
             # conflicts.
             for incompatibility in reversed(self._incompatibilities[package]):
-                if any(
-                    incompatibility in c
-                    for c in self._contradicted_incompatibilities.values()
-                ):
+                if incompatibility in self._contradicted_incompatibilities:
                     continue
 
                 result = self._propagate_incompatibility(incompatibility)
@@ -199,9 +197,10 @@ def _propagate_incompatibility(
                 # If term is already contradicted by _solution, then
                 # incompatibility is contradicted as well and there's nothing new we
                 # can deduce from it.
-                self._contradicted_incompatibilities[self._solution.decision_level].add(
-                    incompatibility
-                )
+                self._contradicted_incompatibilities.add(incompatibility)
+                self._contradicted_incompatibilities_by_level[
+                    self._solution.decision_level
+                ].add(incompatibility)
                 return None
             elif relation == SetRelation.OVERLAPPING:
                 # If more than one term is inconclusive, we can't deduce anything about
@@ -219,9 +218,10 @@ def _propagate_incompatibility(
         if unsatisfied is None:
             return _conflict
 
-        self._contradicted_incompatibilities[self._solution.decision_level].add(
-            incompatibility
-        )
+        self._contradicted_incompatibilities.add(incompatibility)
+        self._contradicted_incompatibilities_by_level[
+            self._solution.decision_level
+        ].add(incompatibility)
 
         adverb = "not " if unsatisfied.is_positive() else ""
         self._log(f"derived: {adverb}{unsatisfied.dependency}")
@@ -318,7 +318,9 @@ def _resolve_conflict(self, incompatibility: Incompatibility) -> Incompatibility
                 for level in range(
                     self._solution.decision_level, previous_satisfier_level, -1
                 ):
-                    self._contradicted_incompatibilities.pop(level, None)
+                    self._contradicted_incompatibilities.difference_update(
+                        self._contradicted_incompatibilities_by_level.pop(level, set()),
+                    )
                     self._dependency_cache.clear_level(level)
 
                 self._solution.backtrack(previous_satisfier_level)