diff --git a/browser/components/loop/content/shared/js/mixins.js b/browser/components/loop/content/shared/js/mixins.js
index f51ea978fa47..9fe560b3a546 100644
--- a/browser/components/loop/content/shared/js/mixins.js
+++ b/browser/components/loop/content/shared/js/mixins.js
@@ -240,6 +240,18 @@ loop.shared.mixins = (function() {
       rootObject.removeEventListener("resize", this.updateVideoContainer);
     },
 
+    /**
+     * Resets the dimensions cache, e.g. for when the session is ended, and
+     * before a new session, so that we always ensure we see an update when a
+     * new session is started.
+     */
+    resetDimensionsCache: function() {
+      this._videoDimensionsCache = {
+        local: {},
+        remote: {}
+      };
+    },
+
     /**
      * Whenever the dimensions change of a video stream, this function is called
      * by `updateVideoDimensions` to store the new values and notifies the callee
diff --git a/browser/components/loop/standalone/content/js/standaloneRoomViews.js b/browser/components/loop/standalone/content/js/standaloneRoomViews.js
index 61b57c2691a0..d4c893ed8dbc 100644
--- a/browser/components/loop/standalone/content/js/standaloneRoomViews.js
+++ b/browser/components/loop/standalone/content/js/standaloneRoomViews.js
@@ -383,6 +383,12 @@ loop.standaloneRoomViews = (function(mozL10n) {
         this.updateVideoContainer();
       }
 
+      if (nextState.roomState === ROOM_STATES.INIT ||
+          nextState.roomState === ROOM_STATES.GATHER ||
+          nextState.roomState === ROOM_STATES.READY) {
+        this.resetDimensionsCache();
+      }
+
       // When screen sharing stops.
       if (this.state.receivingScreenShare && !nextState.receivingScreenShare) {
         // Remove the custom screenshare styles on the remote camera.
diff --git a/browser/components/loop/standalone/content/js/standaloneRoomViews.jsx b/browser/components/loop/standalone/content/js/standaloneRoomViews.jsx
index d43c26300aba..7340c366f3c1 100644
--- a/browser/components/loop/standalone/content/js/standaloneRoomViews.jsx
+++ b/browser/components/loop/standalone/content/js/standaloneRoomViews.jsx
@@ -383,6 +383,12 @@ loop.standaloneRoomViews = (function(mozL10n) {
         this.updateVideoContainer();
       }
 
+      if (nextState.roomState === ROOM_STATES.INIT ||
+          nextState.roomState === ROOM_STATES.GATHER ||
+          nextState.roomState === ROOM_STATES.READY) {
+        this.resetDimensionsCache();
+      }
+
       // When screen sharing stops.
       if (this.state.receivingScreenShare && !nextState.receivingScreenShare) {
         // Remove the custom screenshare styles on the remote camera.
diff --git a/browser/components/loop/test/standalone/standaloneRoomViews_test.js b/browser/components/loop/test/standalone/standaloneRoomViews_test.js
index f0c114913a14..86c4e291ac41 100644
--- a/browser/components/loop/test/standalone/standaloneRoomViews_test.js
+++ b/browser/components/loop/test/standalone/standaloneRoomViews_test.js
@@ -214,6 +214,19 @@ describe("loop.standaloneRoomViews", function() {
 
           sinon.assert.calledOnce(view.updateVideoContainer);
       });
+
+      it("should reset the video dimensions cache when the gather state is entered", function() {
+        activeRoomStore.setStoreState({roomState: ROOM_STATES.SESSION_CONNECTED});
+
+        var view = mountTestComponent();
+
+        activeRoomStore.setStoreState({roomState: ROOM_STATES.GATHER});
+
+        expect(view._videoDimensionsCache).eql({
+          local: {},
+          remote: {}
+        });
+      })
     });
 
     describe("#publishStream", function() {