diff --git a/tracker/tracker/src/main/modules/cssrules.ts b/tracker/tracker/src/main/modules/cssrules.ts
index 10a072b4e..8e2217017 100644
--- a/tracker/tracker/src/main/modules/cssrules.ts
+++ b/tracker/tracker/src/main/modules/cssrules.ts
@@ -17,20 +17,19 @@ export default function (app: App | null) {
     return
   }
 
-  const sendInserDeleteRule = app.safe(
-    (stylesheet: CSSStyleSheet, index: number, rule?: string) => {
-      const sheetID = styleSheetIDMap.get(stylesheet)
-      if (!sheetID) {
-        app.debug.warn('No sheedID found', stylesheet, styleSheetIDMap)
-        return
-      }
-      if (typeof rule === 'string') {
-        app.send(AdoptedSSInsertRuleURLBased(sheetID, rule, index, app.getBaseHref()))
-      } else {
-        app.send(AdoptedSSDeleteRule(sheetID, index))
-      }
-    },
-  )
+  const sendInserDeleteRule = app.safe((sheet: CSSStyleSheet, index: number, rule?: string) => {
+    const sheetID = styleSheetIDMap.get(sheet)
+    if (!sheetID) {
+      app.debug.log('StyleSheet not registered ', sheet, sheet.ownerNode)
+      // Sheet haven't been registered yet. Rules will be sent on registration.
+      return
+    }
+    if (typeof rule === 'string') {
+      app.send(AdoptedSSInsertRuleURLBased(sheetID, rule, index, app.getBaseHref()))
+    } else {
+      app.send(AdoptedSSDeleteRule(sheetID, index))
+    }
+  })
 
   // TODO: proper rule insertion/removal (how?)
   const sendReplaceGroupingRule = app.safe((rule: CSSGroupingRule) => {
@@ -62,22 +61,22 @@ export default function (app: App | null) {
     const { insertRule: groupInsertRule, deleteRule: groupDeleteRule } =
       context.CSSGroupingRule.prototype
 
-    context.CSSStyleSheet.prototype.insertRule = function (rule: string, index = 0) {
+    context.CSSStyleSheet.prototype.insertRule = function (rule: string, index = 0): number {
       sendInserDeleteRule(this, index, rule)
-      return insertRule.call(this, rule, index) as number
+      return insertRule.call(this, rule, index)
     }
-    context.CSSStyleSheet.prototype.deleteRule = function (index: number) {
+    context.CSSStyleSheet.prototype.deleteRule = function (index: number): void {
       sendInserDeleteRule(this, index)
-      return deleteRule.call(this, index) as number
+      return deleteRule.call(this, index)
     }
 
-    context.CSSGroupingRule.prototype.insertRule = function (rule: string, index = 0) {
+    context.CSSGroupingRule.prototype.insertRule = function (rule: string, index = 0): number {
       const result = groupInsertRule.call(this, rule, index) as number
       sendReplaceGroupingRule(this)
       return result
     }
-    context.CSSGroupingRule.prototype.deleteRule = function (index = 0) {
-      const result = groupDeleteRule.call(this, index) as number
+    context.CSSGroupingRule.prototype.deleteRule = function (index = 0): void {
+      const result = groupDeleteRule.call(this, index) as void
       sendReplaceGroupingRule(this)
       return result
     }
@@ -102,6 +101,7 @@ export default function (app: App | null) {
     const sheetID = nextID()
     styleSheetIDMap.set(sheet, sheetID)
     app.send(AdoptedSSAddOwner(sheetID, nodeID))
+    app.debug.log('StyleSheet registered ', sheet, node)
 
     const rules = sheet.cssRules
     for (let i = 0; i < rules.length; i++) {