diff --git a/src/lib/core/overlay/_overlay.scss b/src/lib/core/overlay/_overlay.scss
index 032376df0e8..ea5034b7ff8 100644
--- a/src/lib/core/overlay/_overlay.scss
+++ b/src/lib/core/overlay/_overlay.scss
@@ -9,10 +9,8 @@
     // The container should be the size of the viewport.
     top: 0;
     left: 0;
-
-    // Note: we prefer viewport units, because they aren't being offset by the global scrollbar.
-    height: 100vh;
-    width: 100vw;
+    height: 100%;
+    width: 100%;
   }
 
   // The overlay-container is an invisible element which contains all individual overlays.
diff --git a/src/lib/core/overlay/position/connected-position-strategy.spec.ts b/src/lib/core/overlay/position/connected-position-strategy.spec.ts
index c21fe16ec2f..e978d7d69e8 100644
--- a/src/lib/core/overlay/position/connected-position-strategy.spec.ts
+++ b/src/lib/core/overlay/position/connected-position-strategy.spec.ts
@@ -433,7 +433,7 @@ describe('ConnectedPositionStrategy', () => {
         let overlayRect = overlayElement.getBoundingClientRect();
 
         expect(Math.floor(overlayRect.top)).toBe(Math.floor(originRect.bottom));
-        expect(Math.floor(overlayRect.right)).toBe(Math.floor(originRect.left));
+        expect(Math.round(overlayRect.right)).toBe(Math.round(originRect.left));
       });
 
       it('should position above, right aligned', () => {
@@ -445,8 +445,8 @@ describe('ConnectedPositionStrategy', () => {
         strategy.apply(overlayElement);
 
         let overlayRect = overlayElement.getBoundingClientRect();
-        expect(Math.floor(overlayRect.bottom)).toBe(Math.floor(originRect.top));
-        expect(Math.floor(overlayRect.right)).toBe(Math.floor(originRect.right));
+        expect(Math.round(overlayRect.bottom)).toBe(Math.round(originRect.top));
+        expect(Math.round(overlayRect.right)).toBe(Math.round(originRect.right));
       });
 
       it('should position below, centered', () => {
diff --git a/src/lib/core/overlay/position/connected-position-strategy.ts b/src/lib/core/overlay/position/connected-position-strategy.ts
index a11b5fdf3ee..be515bcb1ce 100644
--- a/src/lib/core/overlay/position/connected-position-strategy.ts
+++ b/src/lib/core/overlay/position/connected-position-strategy.ts
@@ -354,7 +354,6 @@ export class ConnectedPositionStrategy implements PositionStrategy {
       overlayRect: ClientRect,
       overlayPoint: Point,
       pos: ConnectionPositionPair) {
-    const  viewport = this._viewportRuler.getViewportRect();
 
     // We want to set either `top` or `bottom` based on whether the overlay wants to appear above
     // or below the origin and the direction in which the element will expand.
@@ -364,7 +363,7 @@ export class ConnectedPositionStrategy implements PositionStrategy {
     // from the bottom of the viewport rather than the top.
     let y = verticalStyleProperty === 'top' ?
         overlayPoint.y :
-        viewport.height - (overlayPoint.y + overlayRect.height);
+        document.documentElement.clientHeight - (overlayPoint.y + overlayRect.height);
 
     // We want to set either `left` or `right` based on whether the overlay wants to appear "before"
     // or "after" the origin, which determines the direction in which the element will expand.
@@ -381,7 +380,7 @@ export class ConnectedPositionStrategy implements PositionStrategy {
     // from the right edge of the viewport rather than the left edge.
     let x = horizontalStyleProperty === 'left' ?
       overlayPoint.x :
-      viewport.width - (overlayPoint.x + overlayRect.width);
+      document.documentElement.clientWidth - (overlayPoint.x + overlayRect.width);
 
 
     // Reset any existing styles. This is necessary in case the preferred position has