diff --git a/Libraries/WebSocket/RCTWebSocketExecutor.m b/Libraries/WebSocket/RCTWebSocketExecutor.m
index b256374fc59bf7..06217d886abeef 100644
--- a/Libraries/WebSocket/RCTWebSocketExecutor.m
+++ b/Libraries/WebSocket/RCTWebSocketExecutor.m
@@ -158,10 +158,7 @@ - (void)sendMessage:(NSDictionary<NSString *, id> *)message onReply:(RCTWSMessag
 
   dispatch_async(_jsQueue, ^{
     if (!self.valid) {
-      NSError *error = [NSError errorWithDomain:@"WS" code:1 userInfo:@{
-        NSLocalizedDescriptionKey: @"Runtime is not ready for debugging. Make sure Packager server is running."
-      }];
-      callback(error, nil);
+      callback(RCTErrorWithMessage(@"Runtime is not ready for debugging. Make sure Packager server is running."), nil);
       return;
     }
 
@@ -180,8 +177,13 @@ - (void)executeApplicationScript:(NSData *)script sourceURL:(NSURL *)URL onCompl
     @"url": RCTNullIfNil(URL.absoluteString),
     @"inject": _injectedObjects,
   };
-  [self sendMessage:message onReply:^(NSError *error, NSDictionary<NSString *, id> *reply) {
-    onComplete(error);
+  [self sendMessage:message onReply:^(NSError *socketError, NSDictionary<NSString *, id> *reply) {
+    if (socketError) {
+      onComplete(socketError);
+    } else {
+      NSString *error = reply[@"error"];
+      onComplete(error ? RCTErrorWithMessage(error) : nil);
+    }
   }];
 }
 
@@ -218,9 +220,10 @@ - (void)_executeJSCall:(NSString *)method arguments:(NSArray *)arguments callbac
       return;
     }
 
-    NSString *result = reply[@"result"];
-    id objcValue = RCTJSONParse(result, NULL);
-    onComplete(objcValue, nil);
+    NSError *jsonError;
+    id result = RCTJSONParse(reply[@"result"], &jsonError);
+    NSString *error = reply[@"error"];
+    onComplete(result, error ? RCTErrorWithMessage(error) : jsonError);
   }];
 }
 
diff --git a/local-cli/server/util/debuggerWorker.js b/local-cli/server/util/debuggerWorker.js
index 0feb8c079241a9..c05f558d87962b 100644
--- a/local-cli/server/util/debuggerWorker.js
+++ b/local-cli/server/util/debuggerWorker.js
@@ -39,7 +39,7 @@ onmessage = (function() {
       try {
         importScripts(message.url);
       } catch (err) {
-        error = JSON.stringify(err);
+        error = err.message;
       }
       sendReply(null /* result */, error);
     },
@@ -66,12 +66,17 @@ onmessage = (function() {
     } else {
       // Other methods get called on the bridge
       var returnValue = [[], [], [], 0];
+      var error;
       try {
         if (typeof __fbBatchedBridge === 'object') {
           returnValue = __fbBatchedBridge[object.method].apply(null, object.arguments);
+        } else {
+          error = 'Failed to call function, __fbBatchedBridge is undefined';
         }
+      } catch (err) {
+        error = err.message;
       } finally {
-        sendReply(JSON.stringify(returnValue));
+        sendReply(JSON.stringify(returnValue), error);
       }
     }
   };