diff --git a/package-lock.json b/package-lock.json
index fc620d2..385ff7e 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "tempo-monorepo",
-  "version": "3.4.0",
+  "version": "3.5.1",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "tempo-monorepo",
-      "version": "3.4.0",
+      "version": "3.5.1",
       "workspaces": [
         "packages/*"
       ],
@@ -10149,7 +10149,7 @@
     },
     "packages/library": {
       "name": "@magmacomputing/library",
-      "version": "3.4.0",
+      "version": "3.5.1",
       "license": "MIT",
       "dependencies": {
         "tslib": "^2.8.1"
@@ -10160,7 +10160,7 @@
     },
     "packages/tempo": {
       "name": "@magmacomputing/tempo",
-      "version": "3.4.0",
+      "version": "3.5.2",
       "license": "MIT",
       "dependencies": {
         "tslib": "^2.8.1"
diff --git a/package.json b/package.json
index 483a4aa..e532b8a 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "tempo-monorepo",
-  "version": "3.5.0",
+  "version": "3.5.1",
   "private": true,
   "engines": {
     "node": ">=20.0.0"
diff --git a/packages/library/package.json b/packages/library/package.json
index a7e24fe..e18e5c4 100644
--- a/packages/library/package.json
+++ b/packages/library/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@magmacomputing/library",
-  "version": "3.5.0",
+  "version": "3.5.1",
   "description": "Shared utility library for Tempo",
   "author": "Magma Computing Solutions",
   "license": "MIT",
diff --git a/packages/tempo/CHANGELOG.md b/packages/tempo/CHANGELOG.md
index 205a545..be609ae 100644
--- a/packages/tempo/CHANGELOG.md
+++ b/packages/tempo/CHANGELOG.md
@@ -6,6 +6,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [3.5.1] - 2026-06-28
+
+### Fixed
+- **Term Registration Resilience**: Hardened `Tempo.extend` with structural deduplication to safely ignore redundant registrations of identical core terms. This prevents edge-case term collisions (e.g., `qtr`) in mixed module-loader environments like Vitest where Node ESM and Vite may evaluate plugins multiple times.
+
 ## [3.5.0] - 2026-06-28
 
 ### Added
diff --git a/packages/tempo/package.json b/packages/tempo/package.json
index a01dffe..70b7e1c 100644
--- a/packages/tempo/package.json
+++ b/packages/tempo/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@magmacomputing/tempo",
-  "version": "3.5.0",
+  "version": "3.5.1",
   "engines": {
     "node": ">=20.0.0"
   },
diff --git a/packages/tempo/src/tempo.class.ts b/packages/tempo/src/tempo.class.ts
index dda8535..16349a6 100644
--- a/packages/tempo/src/tempo.class.ts
+++ b/packages/tempo/src/tempo.class.ts
@@ -572,13 +572,25 @@ export class Tempo {
 
 						if (Tempo._termMap.get(config.key) === config) return;
 						if (Tempo._termMap.has(config.key)) {
+							const existing = Tempo._termMap.get(config.key);
+							const rangesMatch = JSON.stringify(existing?.ranges) === JSON.stringify(config.ranges);
+							if (existing?.scope === config.scope && existing?.description === config.description && rangesMatch) {
+								logDebug(`[Tempo#extend] Duplicate term registration ignored for key: "${config.key}"`, state.config);
+								return;
+							}
 							logError(`[Tempo#extend] Term collision on key: "${config.key}". Registration aborted.`, state.config);
 							return;
 						}
 						if (config.scope && Tempo._termMap.get(config.scope) === config) { /* continue */ }
 						else if (config.scope && Tempo._termMap.has(config.scope)) {
-							logError(`[Tempo#extend] Term collision on scope: "${config.scope}". Registration aborted.`, state.config);
-							return;
+							const existingScope = Tempo._termMap.get(config.scope);
+							const rangesMatch = JSON.stringify(existingScope?.ranges) === JSON.stringify(config.ranges);
+							if (existingScope?.key === config.key && existingScope?.description === config.description && rangesMatch) {
+								/* continue */
+							} else {
+								logError(`[Tempo#extend] Term collision on scope: "${config.scope}". Registration aborted.`, state.config);
+								return;
+							}
 						}
 
 						Tempo._termMap.set(config.key, config);
@@ -596,13 +608,11 @@ export class Tempo {
 									if (r.key) {
 										let val: string | undefined;
 										if (isDefined(r.hour)) {
-											if (Number.isInteger(r.hour) && r.hour >= 0 && r.hour <= 23) {
+											if (Number.isInteger(r.hour) && r.hour >= 0 && r.hour <= 23)
 												val = `${r.hour}:${pad(r.minute ?? 0)}`;
-											}
 										} else if (r.month) {
-											if (Number.isInteger(r.month) && r.month >= 1 && r.month <= 12) {
+											if (Number.isInteger(r.month) && r.month >= 1 && r.month <= 12)
 												val = `${pad(r.day ?? 1)} ${monthKeys[r.month - 1]}`;
-											}
 										}
 
 										if (val) aliases.push([r.key, val]);
diff --git a/packages/tempo/src/tempo.version.ts b/packages/tempo/src/tempo.version.ts
index f3af59d..674c584 100644
--- a/packages/tempo/src/tempo.version.ts
+++ b/packages/tempo/src/tempo.version.ts
@@ -5,4 +5,4 @@
  * ⚠️ This file is auto-updated by `npm run build:version` (see `bin/update-version.mjs`).
  * Do NOT edit manually — your changes will be overwritten on the next build.
  */
-export const TEMPO_VERSION = '3.5.0';
+export const TEMPO_VERSION = '3.5.1';