diff --git a/runtime/observatory/lib/src/debugger/debugger_location.dart b/runtime/observatory/lib/src/debugger/debugger_location.dart
index 9ba4bacfbef..1904e439286 100644
--- a/runtime/observatory/lib/src/debugger/debugger_location.dart
+++ b/runtime/observatory/lib/src/debugger/debugger_location.dart
@@ -75,8 +75,8 @@ class DebuggerLocation {
     if (colStr != null) {
       colStr = colStr.substring(1);
     }
-    var line = int.parse(lineStr, onError: (_) => -1);
-    var col = (colStr != null ? int.parse(colStr, onError: (_) => -1) : null);
+    var line = int.tryParse(lineStr) ?? -1;
+    var col = (colStr != null ? int.tryParse(colStr) ?? -1 : null);
     if (line == -1) {
       return new Future.value(
           new DebuggerLocation.error("Line '${lineStr}' must be an integer"));
diff --git a/runtime/observatory/lib/src/elements/debugger.dart b/runtime/observatory/lib/src/elements/debugger.dart
index 5cc68965724..5b155439528 100644
--- a/runtime/observatory/lib/src/elements/debugger.dart
+++ b/runtime/observatory/lib/src/elements/debugger.dart
@@ -1008,7 +1008,7 @@ class IsolateCommand extends DebuggerCommand {
       return new Future.value(null);
     }
     var arg = args[0].trim();
-    var num = int.parse(arg, onError: (_) => null);
+    var num = int.tryParse(arg);
 
     var candidate;
     for (var isolate in debugger.vm.isolates) {
diff --git a/runtime/observatory/lib/src/repositories/target.dart b/runtime/observatory/lib/src/repositories/target.dart
index 35d0ddee2ac..56c6246be22 100644
--- a/runtime/observatory/lib/src/repositories/target.dart
+++ b/runtime/observatory/lib/src/repositories/target.dart
@@ -117,7 +117,7 @@ class TargetRepository implements M.TargetRepository {
     final Uri wsAddress = new Uri(
       scheme: 'ws',
       host: host ?? serverAddress.host,
-      port: int.parse(port ?? '', onError: (_) => serverAddress.port),
+      port: int.tryParse(port ?? '') ?? serverAddress.port,
       path: '/ws',
     );
     return wsAddress.toString();
diff --git a/runtime/observatory/lib/src/service/object.dart b/runtime/observatory/lib/src/service/object.dart
index 58503e14f87..38c9a91081e 100644
--- a/runtime/observatory/lib/src/service/object.dart
+++ b/runtime/observatory/lib/src/service/object.dart
@@ -1624,7 +1624,7 @@ class Isolate extends ServiceObjectOwner implements M.Isolate {
   void _update(Map map, bool mapIsRef) {
     name = map['name'];
     vmName = map.containsKey('_vmName') ? map['_vmName'] : name;
-    number = int.parse(map['number'], onError: (_) => null);
+    number = int.tryParse(map['number']);
     if (mapIsRef) {
       return;
     }
@@ -1632,7 +1632,7 @@ class Isolate extends ServiceObjectOwner implements M.Isolate {
     loading = false;
     runnable = map['runnable'] == true;
     _upgradeCollection(map, isolate);
-    originNumber = int.parse(map['_originNumber'], onError: (_) => null);
+    originNumber = int.tryParse(map['_originNumber']);
     rootLibrary = map['rootLib'];
     if (map['entry'] != null) {
       entry = map['entry'];