diff --git a/LabPurchasing/resources/queries/labpurchasing/purchases.js b/LabPurchasing/resources/queries/labpurchasing/purchases.js
index 602ce37ff..cbcfa7d50 100644
--- a/LabPurchasing/resources/queries/labpurchasing/purchases.js
+++ b/LabPurchasing/resources/queries/labpurchasing/purchases.js
@@ -4,6 +4,31 @@ var console = require("console");
 var triggerHelper = new org.labkey.labpurchasing.LabPurchasingTriggerHelper(LABKEY.Security.currentUser.id, LABKEY.Security.currentContainer.id);
 
 function beforeInsert(row, errors){
+    beforeUpsert(row, errors)
+}
+
+function beforeUpdate(row, oldRow, errors){
+    beforeUpsert(row, errors)
+}
+
+function beforeUpsert(row, errors){
+    // Validate requestor:
+    if (row.requestor) {
+        if (!isNaN(row.requestor) && !triggerHelper.isValidUserId(row.requestor)) {
+            errors.requestor = 'Unknown userId for requestor: ' + row.requestor;
+        }
+        // Try to resolve strings:
+        else if (isNaN(row.requestor)) {
+            var id = triggerHelper.resolveUserId(String(row.requestor));
+            if (!id) {
+                errors.requestor = 'Unknown userId for requestor: ' + row.requestor;
+            }
+            else {
+                row.requestor = id;
+            }
+        }
+    }
+
     // The purpose of this is to allow the user to provide a string value for
     // vendorId or vendorName, and attempt to resolve this against known vendors:
     if (!row.vendorId || isNaN(row.vendorId)) {
diff --git a/LabPurchasing/src/org/labkey/labpurchasing/LabPurchasingTriggerHelper.java b/LabPurchasing/src/org/labkey/labpurchasing/LabPurchasingTriggerHelper.java
index f79c3688e..2625a0dca 100644
--- a/LabPurchasing/src/org/labkey/labpurchasing/LabPurchasingTriggerHelper.java
+++ b/LabPurchasing/src/org/labkey/labpurchasing/LabPurchasingTriggerHelper.java
@@ -112,4 +112,16 @@ public void sendNotifications(List<Integer> rowIds) {
             _log.error("Unable to send purchasing email", e);
         }
     }
+
+    public boolean isValidUserId(int userId)
+    {
+        return UserManager.getUser(userId) != null;
+    }
+
+    public Integer resolveUserId(String userNameOrEmail)
+    {
+        User u = UserManager.getUserByDisplayName(userNameOrEmail);
+
+        return u == null ? null : u.getUserId();
+    }
 }