diff --git a/lang/en.json b/lang/en.json
index 01eb8bb..adfac00 100644
--- a/lang/en.json
+++ b/lang/en.json
@@ -16,6 +16,7 @@
   "SIMPLE.NotifyGroupAlphanumeric": "Attribute group names may not contain spaces or periods.",
   "SIMPLE.NotifyGroupReserved": "Attribute group \"{key}\" is reserved and cannot be used.",
   "SIMPLE.NotifyAttrDuplicate": "Attribute key already exists as a group.",
+  "SIMPLE.NotifyAttrInvalid": "Attribute keys may not contain spaces or periods.",
 
   "SIMPLE.ResourceMin": "Min",
   "SIMPLE.ResourceValue": "Value",
@@ -35,4 +36,4 @@
 
   "SIMPLE.Create": "Create",
   "SIMPLE.New": "New"
-}
\ No newline at end of file
+}
diff --git a/module/helper.js b/module/helper.js
index 66a9f92..5f310e6 100644
--- a/module/helper.js
+++ b/module/helper.js
@@ -429,8 +429,7 @@ export class EntitySheetHelper {
           group = v[attrKey]['group'];
           groupKeys.push(group);
           let attr = v[attrKey];
-          let k = v[attrKey]["key"] ? v[attrKey]["key"].trim() : attrKey.trim();
-          if ( /[\s\.]/.test(k) )  return ui.notifications.error("Attribute keys may not contain spaces or periods");
+          const k = this.cleanKey(v[attrKey]["key"] ? v[attrKey]["key"].trim() : attrKey.trim());
           delete attr["key"];
           // Add the new attribute if it's grouped, but we need to build the nested structure first.
           if ( !obj[group] ) {
@@ -441,8 +440,7 @@ export class EntitySheetHelper {
       }
       // Handle attribute keys for ungrouped attributes.
       else {
-        let k = v["key"].trim();
-        if ( /[\s\.]/.test(k) )  return ui.notifications.error("Attribute keys may not contain spaces or periods");
+        const k = this.cleanKey(v["key"].trim());
         delete v["key"];
         // Add the new attribute only if it's ungrouped.
         if ( !group ) {
@@ -588,4 +586,17 @@ export class EntitySheetHelper {
       foundry.utils.setProperty(attrs, attr, Math.clamped(value, current.min || 0, current.max || 0));
     }
   }
+
+  /* -------------------------------------------- */
+
+  /**
+   * Clean an attribute key, emitting an error if it contained invalid characters.
+   * @param {string} key  The key to clean.
+   * @returns {string}
+   */
+  static cleanKey(key) {
+    const clean = key.replace(/[\s.]/g, "");
+    if ( clean !== key ) ui.notifications.error("SIMPLE.NotifyAttrInvalid", { localize: true });
+    return clean;
+  }
 }