diff --git a/src/components/structures/ScrollPanel.js b/src/components/structures/ScrollPanel.js
index f7f954bc0f..31ac59c730 100644
--- a/src/components/structures/ScrollPanel.js
+++ b/src/components/structures/ScrollPanel.js
@@ -26,6 +26,9 @@ var DEBUG_SCROLL = false;
 // The amount of extra scroll distance to allow prior to unfilling.
 // See _getExcessHeight.
 const UNPAGINATION_PADDING = 1500;
+// The number of milliseconds to debounce calls to onUnfillRequest, to prevent
+// many scroll events causing many unfilling requests.
+const UNFILL_REQUEST_DEBOUNCE_MS = 200;
 
 if (DEBUG_SCROLL) {
     // using bind means that we get to keep useful line numbers in the console
@@ -367,8 +370,9 @@ module.exports = React.createClass({
                 clearTimeout(this._unfillDebouncer);
             }
             this._unfillDebouncer = setTimeout(() => {
+                this._unfillDebouncer = null;
                 this.props.onUnfillRequest(backwards, markerScrollToken);
-            }, 200);
+            }, UNFILL_REQUEST_DEBOUNCE_MS);
         }
     },