diff --git a/src/extensions/scratch3_makeymakey/index.js b/src/extensions/scratch3_makeymakey/index.js
index 59c692918..79a73e246 100644
--- a/src/extensions/scratch3_makeymakey/index.js
+++ b/src/extensions/scratch3_makeymakey/index.js
@@ -86,6 +86,9 @@ class Scratch3MakeyMakeyBlocks {
         this.keyPressed = this.keyPressed.bind(this);
         this.runtime.on('KEY_PRESSED', this.keyPressed);
 
+        this._clearkeyPressBuffer = this._clearkeyPressBuffer.bind(this);
+        this.runtime.on('PROJECT_STOP_ALL', this._clearkeyPressBuffer);
+
         /*
          * An object containing a set of sequence objects.
          * These are the key sequences currently being detected by the "when
@@ -337,6 +340,13 @@ class Scratch3MakeyMakeyBlocks {
         }
     }
 
+    /**
+     * Clear the key press buffer.
+     */
+    _clearkeyPressBuffer () {
+        this.keyPressBuffer = [];
+    }
+
     /*
      * Add a key sequence to the set currently being checked on each key press.
      * @param {string} sequenceString a string of space-separated KEY_IDs.