diff --git a/packages/flutter/lib/src/foundation/diagnostics.dart b/packages/flutter/lib/src/foundation/diagnostics.dart
index dc45476..5c0b812 100644
--- a/packages/flutter/lib/src/foundation/diagnostics.dart
+++ b/packages/flutter/lib/src/foundation/diagnostics.dart
@@ -2127,7 +2127,12 @@
 
   @override
   String toString({ DiagnosticLevel minLevel = DiagnosticLevel.debug }) {
-    return toDiagnosticsNode(style: DiagnosticsTreeStyle.singleLine).toString(minLevel: minLevel);
+    String fullString;
+    assert(() {
+      fullString = toDiagnosticsNode(style: DiagnosticsTreeStyle.singleLine).toString(minLevel: minLevel);
+      return true;
+    }());
+    return fullString ?? toStringShort();
   }
 
   /// Returns a debug representation of the object that is used by debugging