diff --git a/src/__tests__/diff.test.ts b/src/__tests__/diff.test.ts
index 0f8587c..8bb1510 100644
--- a/src/__tests__/diff.test.ts
+++ b/src/__tests__/diff.test.ts
@@ -42,14 +42,31 @@ describe('diff', () => {
     expect(report.removed[0].name).toBe('moment');
   });
 
-  it('detects version upgrades', () => {
+  it('detects version upgrades matched by purl (version stripped from key)', () => {
     const a = makesbom([{ name: 'lodash', version: '4.17.20', purl: 'pkg:npm/lodash@4.17.20' }]);
     const b = makesbom([{ name: 'lodash', version: '4.17.21', purl: 'pkg:npm/lodash@4.17.21' }]);
     const report = diff(a, b);
-    // Different purl = treated as add/remove (purl includes version)
-    // With our current purl-based key: 4.17.20 -> removed, 4.17.21 -> added
-    // This is correct behavior — different purls are different packages
-    expect(report.added.length + report.removed.length + report.upgraded.length).toBeGreaterThan(0);
+    // A purl embeds the version, but the same package upgraded is one dependency,
+    // not an unrelated add + remove. The diff strips the version from the purl so
+    // this is reported as a single upgrade.
+    expect(report.added).toHaveLength(0);
+    expect(report.removed).toHaveLength(0);
+    expect(report.upgraded).toHaveLength(1);
+    expect(report.upgraded[0].from).toBe('4.17.20');
+    expect(report.upgraded[0].to).toBe('4.17.21');
+    expect(report.upgraded[0].isMajorBump).toBe(false);
+  });
+
+  it('detects a major-version upgrade of a scoped (namespaced) purl', () => {
+    // The scope "@angular" is percent-encoded as %40 in a purl, so only the
+    // version delimiter is a literal "@" — stripping it must not touch the scope.
+    const a = makesbom([{ name: '@angular/core', version: '15.2.0', purl: 'pkg:npm/%40angular/core@15.2.0' }]);
+    const b = makesbom([{ name: '@angular/core', version: '16.0.0', purl: 'pkg:npm/%40angular/core@16.0.0' }]);
+    const report = diff(a, b);
+    expect(report.added).toHaveLength(0);
+    expect(report.removed).toHaveLength(0);
+    expect(report.upgraded).toHaveLength(1);
+    expect(report.upgraded[0].isMajorBump).toBe(true);
   });
 
   it('detects version upgrades when matched by name (no purl)', () => {
diff --git a/src/diff.ts b/src/diff.ts
index 6540b50..cb77d6d 100644
--- a/src/diff.ts
+++ b/src/diff.ts
@@ -63,13 +63,37 @@ export function diff(a: SBOM, b: SBOM): ChangeReport {
 function buildComponentMap(components: Component[]): Map<string, Component> {
   const map = new Map<string, Component>();
   for (const comp of components) {
-    // Prefer purl as key, fall back to name
-    const key = comp.purl ?? comp.name;
-    map.set(key, comp);
+    map.set(componentKey(comp), comp);
   }
   return map;
 }
 
+/**
+ * Derive a stable, version-independent identity for a component.
+ *
+ * A purl embeds the version (e.g. "pkg:npm/lodash@4.17.21"), so keying the diff
+ * on the raw purl would make every upgrade look like an unrelated remove + add —
+ * defeating the tool's headline "upgraded dependencies" detection. Strip the
+ * version so the same package at two versions maps to one identity. Falls back to
+ * the name (also version-stripped by construction) when no purl is present.
+ */
+function componentKey(comp: Component): string {
+  return comp.purl ? stripPurlVersion(comp.purl) : comp.name;
+}
+
+/**
+ * Remove the version segment from a package URL.
+ *
+ * In a purl the version follows the first *literal* "@"; any "@" inside the
+ * namespace (e.g. an npm scope "@angular") is percent-encoded as "%40", so the
+ * first literal "@" always delimits the version. Qualifiers ("?...") and the
+ * subpath ("#...") are preserved so components that differ only by those are
+ * still distinguished.
+ */
+function stripPurlVersion(purl: string): string {
+  return purl.replace(/@[^?#]*/, '');
+}
+
 /**
  * Returns true if the major version changed (semver-style).
  * Handles versions like "1.2.3", "2.0.0-beta", etc.