diff --git a/.github/scripts/Test-KnowledgeIndex.ps1 b/.github/scripts/Test-KnowledgeIndex.ps1
index 224b010..76896af 100644
--- a/.github/scripts/Test-KnowledgeIndex.ps1
+++ b/.github/scripts/Test-KnowledgeIndex.ps1
@@ -27,6 +27,10 @@ param(
 Set-StrictMode -Version Latest
 $ErrorActionPreference = 'Stop'
 
+# Normalise to an absolute path so Substring-based relative-path derivation
+# below matches the absolute FullName the generator emits (CI passes -Root .).
+$Root = (Resolve-Path -LiteralPath $Root).Path
+
 $generator = Join-Path $Root 'tools/Build-KnowledgeIndex.ps1'
 if (-not (Test-Path $generator)) { throw "Generator not found: $generator" }
 
diff --git a/tools/Build-KnowledgeIndex.ps1 b/tools/Build-KnowledgeIndex.ps1
index 09758b9..5835e5d 100644
--- a/tools/Build-KnowledgeIndex.ps1
+++ b/tools/Build-KnowledgeIndex.ps1
@@ -79,6 +79,10 @@ if (-not $BCQualityRoot) {
 if (-not (Test-Path $BCQualityRoot)) {
     throw "BCQuality root not found: $BCQualityRoot"
 }
+# Normalise to an absolute path: Get-ChildItem.FullName below is always
+# absolute, so Get-RelativePath's Substring needs an absolute root to strip.
+# A relative root (e.g. '.') would otherwise leave the full path intact.
+$BCQualityRoot = (Resolve-Path -LiteralPath $BCQualityRoot).Path
 if (-not $IndexPath) {
     $IndexPath = Join-Path $BCQualityRoot 'knowledge-index.json'
 }