diff --git a/src/chart.ts b/src/chart.ts
index 9464621..68a5d26 100644
--- a/src/chart.ts
+++ b/src/chart.ts
@@ -553,7 +553,11 @@ export class Chart extends EventEmitter.EventEmitter {
         },
         (d: any) => {
           // The key is the function set or other value that uniquely identifies the datum.
-          return d.fn || d.r || d.x || d.text
+          // Add the graphType to the key to handle graphType updates on the same function (#344)
+          return JSON.stringify({
+            function: d.fn || d.r || d.x || d.text,
+            graphType: d.graphType
+          })
         }
       )