diff --git a/dwds/CHANGELOG.md b/dwds/CHANGELOG.md
index 0b4c08223..5b2c18105 100644
--- a/dwds/CHANGELOG.md
+++ b/dwds/CHANGELOG.md
@@ -1,5 +1,10 @@
 ## 24.3.7-wip
 
+- `callServiceExtension` now checks the runtime for the list of registered
+  service extensions. It also now throws a `RPCError` with
+  `RPCErrorKind.kMethodNotFound` when a service extension is not found instead
+  of throwing a JS evaluation error.
+
 ## 24.3.6
 
 - Bump minimum sdk version to 3.7.0
diff --git a/dwds/lib/src/debugging/inspector.dart b/dwds/lib/src/debugging/inspector.dart
index b2a8fcdd1..7128adde0 100644
--- a/dwds/lib/src/debugging/inspector.dart
+++ b/dwds/lib/src/debugging/inspector.dart
@@ -115,8 +115,7 @@ class AppInspector implements AppInspectorInterface {
     await DartUri.initialize();
     DartUri.recordAbsoluteUris(libraries.map((lib) => lib.uri).nonNulls);
     DartUri.recordAbsoluteUris(scripts.map((script) => script.uri).nonNulls);
-
-    isolate.extensionRPCs?.addAll(await _getExtensionRpcs());
+    await getExtensionRpcs();
   }
 
   static IsolateRef _toIsolateRef(Isolate isolate) => IsolateRef(
@@ -760,11 +759,16 @@ class AppInspector implements AppInspectorInterface {
       scriptId == null ? null : _scriptRefsById[scriptId];
 
   /// Runs an eval on the page to compute all existing registered extensions.
-  Future<List<String>> _getExtensionRpcs() async {
+  ///
+  /// Combines this with the RPCs registered in the [isolate]. Use this over
+  /// [Isolate.extensionRPCs] as this computes a live set.
+  ///
+  /// Updates [Isolate.extensionRPCs] to this set.
+  Future<Set<String>> getExtensionRpcs() async {
     final expression =
         globalToolConfiguration.loadStrategy.dartRuntimeDebugger
             .getDartDeveloperExtensionNamesJsExpression();
-    final extensionRpcs = <String>[];
+    final extensionRpcs = <String>{};
     final params = {
       'expression': expression,
       'returnByValue': true,
@@ -784,6 +788,7 @@ class AppInspector implements AppInspectorInterface {
         s,
       );
     }
+    isolate.extensionRPCs = List<String>.of(extensionRpcs);
     return extensionRpcs;
   }
 
diff --git a/dwds/lib/src/services/chrome_proxy_service.dart b/dwds/lib/src/services/chrome_proxy_service.dart
index 93b9f6751..71f496b22 100644
--- a/dwds/lib/src/services/chrome_proxy_service.dart
+++ b/dwds/lib/src/services/chrome_proxy_service.dart
@@ -343,7 +343,7 @@ class ChromeProxyService implements VmServiceInterface {
     // TODO: We shouldn't need to fire these events since they exist on the
     // isolate, but devtools doesn't recognize extensions after a page refresh
     // otherwise.
-    for (final extensionRpc in inspector.isolate.extensionRPCs ?? []) {
+    for (final extensionRpc in await inspector.getExtensionRpcs()) {
       _streamNotify(
         'Isolate',
         Event(
@@ -509,6 +509,13 @@ class ChromeProxyService implements VmServiceInterface {
         v is String ? v : jsonEncode(v),
       ),
     );
+    if (!(await inspector.getExtensionRpcs()).contains(method)) {
+      throw RPCError(
+        method,
+        RPCErrorKind.kMethodNotFound.code,
+        'Unknown service method: $method',
+      );
+    }
     final expression = globalToolConfiguration.loadStrategy.dartRuntimeDebugger
         .invokeExtensionJsExpression(method, jsonEncode(stringArgs));
     final result = await inspector.jsEvaluate(expression, awaitPromise: true);
diff --git a/dwds/test/common/chrome_proxy_service_common.dart b/dwds/test/common/chrome_proxy_service_common.dart
index 1c165f620..178aed35a 100644
--- a/dwds/test/common/chrome_proxy_service_common.dart
+++ b/dwds/test/common/chrome_proxy_service_common.dart
@@ -298,6 +298,20 @@ void runTests({
           ),
         },
       );
+
+      test('not found', () async {
+        final serviceMethod = 'ext.test.missingServiceExtension';
+        expect(
+          service.callServiceExtension(serviceMethod),
+          throwsA(
+            predicate(
+              (dynamic error) =>
+                  error is RPCError &&
+                  error.code == RPCErrorKind.kMethodNotFound.code,
+            ),
+          ),
+        );
+      });
     });
 
     group('VMTimeline', () {