diff --git a/src/NodeSlot.ts b/src/NodeSlot.ts
index 263d6cd00d..c41d833b21 100644
--- a/src/NodeSlot.ts
+++ b/src/NodeSlot.ts
@@ -97,6 +97,7 @@ export abstract class NodeSlot implements INodeSlot {
   nameLocked?: boolean
   pos?: Point
   widget?: IWidget
+  hasErrors?: boolean
 
   constructor(slot: INodeSlot) {
     Object.assign(this, slot)
@@ -237,6 +238,15 @@ export abstract class NodeSlot implements INodeSlot {
       }
     }
 
+    // Draw a red circle if the slot has errors.
+    if (this.hasErrors) {
+      ctx.lineWidth = 2
+      ctx.strokeStyle = "red"
+      ctx.beginPath()
+      ctx.arc(pos[0], pos[1], 12, 0, Math.PI * 2)
+      ctx.stroke()
+    }
+
     // Restore the original fillStyle and strokeStyle
     ctx.fillStyle = originalFillStyle
     ctx.strokeStyle = originalStrokeStyle
diff --git a/src/interfaces.ts b/src/interfaces.ts
index 47cb66b85a..f5c4d25d1e 100644
--- a/src/interfaces.ts
+++ b/src/interfaces.ts
@@ -291,6 +291,10 @@ export interface INodeSlot {
    * This is calculated at runtime; it is **not** serialized.
    */
   _floatingLinks?: Set<LLink>
+  /**
+   * Whether the slot has errors. It is **not** serialized.
+   */
+  hasErrors?: boolean
 }
 
 export interface INodeFlags {