diff --git a/packages/flutter/lib/src/animation/animation_controller.dart b/packages/flutter/lib/src/animation/animation_controller.dart
index da359a0780e..73cd31c85e1 100644
--- a/packages/flutter/lib/src/animation/animation_controller.dart
+++ b/packages/flutter/lib/src/animation/animation_controller.dart
@@ -842,7 +842,13 @@ class AnimationController extends Animation<double>
   String toStringDetails() {
     final String paused = isAnimating ? '' : '; paused';
     final String ticker = _ticker == null ? '; DISPOSED' : (_ticker!.muted ? '; silenced' : '');
-    final String label = debugLabel == null ? '' : '; for $debugLabel';
+    String label = '';
+    assert(() {
+      if (debugLabel != null) {
+        label = '; for $debugLabel';
+      }
+      return true;
+    }());
     final String more = '${super.toStringDetails()} ${value.toStringAsFixed(3)}';
     return '$more$paused$ticker$label';
   }