diff --git a/internal/codeguard/checks/design/design_change_impact.go b/internal/codeguard/checks/design/design_change_impact.go
index 0a677dd..033fec3 100644
--- a/internal/codeguard/checks/design/design_change_impact.go
+++ b/internal/codeguard/checks/design/design_change_impact.go
@@ -29,8 +29,9 @@ func changeImpactFindings(env support.Context, graphs []targetModuleGraph) []cor
 	entries := make([]core.ChangeImpactEntry, 0)
 	findings := make([]core.Finding, 0)
 	for _, item := range graphs {
+		reverse := item.graph.reverseDependencies()
 		for _, changed := range env.ChangedFiles {
-			entry, ok := changeImpactEntry(item, changed)
+			entry, ok := changeImpactEntry(item, reverse, changed)
 			if !ok {
 				continue
 			}
@@ -46,12 +47,12 @@ func changeImpactFindings(env support.Context, graphs []targetModuleGraph) []cor
 	return findings
 }
 
-func changeImpactEntry(item targetModuleGraph, changed string) (core.ChangeImpactEntry, bool) {
+func changeImpactEntry(item targetModuleGraph, reverse map[string][]string, changed string) (core.ChangeImpactEntry, bool) {
 	module, ok := item.graph.fileToModule[filepath.ToSlash(changed)]
 	if !ok {
 		return core.ChangeImpactEntry{}, false
 	}
-	dependents := item.graph.transitiveDependents(module)
+	dependents := support.TransitiveDependents(reverse, module)
 	return core.ChangeImpactEntry{
 		Target:               item.target.Name,
 		Language:             item.graph.language,
diff --git a/internal/codeguard/checks/design/design_dependency_graph.go b/internal/codeguard/checks/design/design_dependency_graph.go
index 1990b5e..66a0215 100644
--- a/internal/codeguard/checks/design/design_dependency_graph.go
+++ b/internal/codeguard/checks/design/design_dependency_graph.go
@@ -1,10 +1,6 @@
 package design
 
-import (
-	"sort"
-
-	"github.com/devr-tools/codeguard/internal/codeguard/checks/support"
-)
+import "sort"
 
 // moduleGraph is a language-neutral module import graph used for cycle,
 // god-module, and change-impact analysis across languages.
@@ -118,14 +114,15 @@ func (g *moduleGraph) fanCounts() (map[string]int, map[string]int) {
 	return fanOut, fanIn
 }
 
-// transitiveDependents returns every module that reaches the given module
-// through one or more import edges, sorted by name.
-func (g *moduleGraph) transitiveDependents(module string) []string {
+// reverseDependencies builds the reverse adjacency list shared by change-impact
+// traversals. Callers should build it once after graph construction rather than
+// rebuilding it for every changed module.
+func (g *moduleGraph) reverseDependencies() map[string][]string {
 	reverse := make(map[string][]string, len(g.modules))
 	for from, node := range g.modules {
 		for _, edge := range node.edges {
 			reverse[edge.to] = append(reverse[edge.to], from)
 		}
 	}
-	return support.TransitiveDependents(reverse, module)
+	return reverse
 }