diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index af6a39ef7204..99b9aee43530 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -825,6 +825,33 @@ ApplyRectMultiplier(nsRect aRect, float aMultiplier)
   return nsRect(ceil(newX), ceil(newY), floor(newWidth), floor(newHeight));
 }
 
+// Return the maximum displayport size, based on the LayerManager's maximum
+// supported texture size. The result is in app units.
+static nscoord
+GetMaxDisplayPortSize(nsIContent* aContent)
+{
+  MOZ_ASSERT(!gfxPrefs::LayersTilesEnabled(), "Do not clamp displayports if tiling is enabled");
+
+  nsIFrame* frame = aContent->GetPrimaryFrame();
+  if (!frame) {
+    return nscoord_MAX;
+  }
+  frame = nsLayoutUtils::GetDisplayRootFrame(frame);
+
+  nsIWidget* widget = frame->GetNearestWidget();
+  if (!widget) {
+    return nscoord_MAX;
+  }
+  LayerManager* lm = widget->GetLayerManager();
+  if (!lm) {
+    return nscoord_MAX;
+  }
+  nsPresContext* presContext = frame->PresContext();
+
+  uint32_t maxSizeInDevPixels = lm->GetMaxTextureSize();
+  return presContext->DevPixelsToAppUnits(maxSizeInDevPixels);
+}
+
 static nsRect
 GetDisplayPortFromRectData(nsIContent* aContent,
                            DisplayPortPropertyData* aRectData,
@@ -900,24 +927,23 @@ GetDisplayPortFromMarginsData(nsIContent* aContent,
   ScreenRect screenRect = LayoutDeviceRect::FromAppUnits(base, auPerDevPixel)
                         * parentRes;
 
-  // Expand the rect by the margins
-  screenRect.Inflate(aMarginsData->mMargins);
+  if (gfxPrefs::LayersTilesEnabled()) {
+    // Note on the correctness of applying the alignment in Screen space:
+    //   The correct space to apply the alignment in would be Layer space, but
+    //   we don't necessarily know the scale to convert to Layer space at this
+    //   point because Layout may not yet have chosen the resolution at which to
+    //   render (it chooses that in FrameLayerBuilder, but this can be called
+    //   during display list building). Therefore, we perform the alignment in
+    //   Screen space, which basically assumes that Layout chose to render at
+    //   screen resolution; since this is what Layout does most of the time,
+    //   this is a good approximation. A proper solution would involve moving
+    //   the choosing of the resolution to display-list building time.
+    int alignmentX = gfxPlatform::GetPlatform()->GetTileWidth();
+    int alignmentY = gfxPlatform::GetPlatform()->GetTileHeight();
 
-  int alignmentX = gfxPlatform::GetPlatform()->GetTileWidth();
-  int alignmentY = gfxPlatform::GetPlatform()->GetTileHeight();
+    // Expand the rect by the margins
+    screenRect.Inflate(aMarginsData->mMargins);
 
-  // And then align it to the requested alignment.
-  // Note on the correctness of applying the alignment in Screen space:
-  //   The correct space to apply the alignment in would be Layer space, but
-  //   we don't necessarily know the scale to convert to Layer space at this
-  //   point because Layout may not yet have chosen the resolution at which to
-  //   render (it chooses that in FrameLayerBuilder, but this can be called
-  //   during display list building). Therefore, we perform the alignment in
-  //   Screen space, which basically assumes that Layout chose to render at
-  //   screen resolution; since this is what Layout does most of the time,
-  //   this is a good approximation. A proper solution would involve moving the
-  //   choosing of the resolution to display-list building time.
-  if (gfxPrefs::LayersTilesEnabled() && (alignmentX > 0 && alignmentY > 0)) {
     // Inflate the rectangle by 1 so that we always push to the next tile
     // boundary. This is desirable to stop from having a rectangle with a
     // moving origin occasionally being smaller when it coincidentally lines
@@ -942,9 +968,38 @@ GetDisplayPortFromMarginsData(nsIContent* aContent,
     float h = alignmentY * ceil(screenRect.YMost() / alignmentY) - y;
     screenRect = ScreenRect(x, y, w, h);
     screenRect -= scrollPosScreen;
+  } else {
+    nscoord maxSizeInAppUnits = GetMaxDisplayPortSize(aContent);
+    if (maxSizeInAppUnits == nscoord_MAX) {
+      // Pick a safe maximum displayport size for sanity purposes. This is the
+      // lowest maximum texture size on tileless-platforms (Windows, D3D10).
+      maxSizeInAppUnits = presContext->DevPixelsToAppUnits(8192);
+    }
+
+    // Find the maximum size in screen pixels.
+    int32_t maxSizeInDevPixels = presContext->AppUnitsToDevPixels(maxSizeInAppUnits);
+    int32_t maxWidthInScreenPixels = floor(double(maxSizeInDevPixels) * res.xScale);
+    int32_t maxHeightInScreenPixels = floor(double(maxSizeInDevPixels) * res.yScale);
+
+    // For each axis, inflate the margins up to the maximum size.
+    const ScreenMargin& margins = aMarginsData->mMargins;
+    if (screenRect.height < maxHeightInScreenPixels) {
+      int32_t budget = maxHeightInScreenPixels - screenRect.height;
+
+      int32_t top = std::min(int32_t(margins.top), budget);
+      screenRect.y -= top;
+      screenRect.height += top + std::min(int32_t(margins.bottom), budget - top);
+    }
+    if (screenRect.width < maxWidthInScreenPixels) {
+      int32_t budget = maxWidthInScreenPixels - screenRect.width;
+
+      int32_t left = std::min(int32_t(margins.left), budget);
+      screenRect.x -= left;
+      screenRect.width += left + std::min(int32_t(margins.right), budget - left);
+    }
   }
 
-  // Convert the aligned rect back into app units
+  // Convert the aligned rect back into app units.
   nsRect result = LayoutDeviceRect::ToAppUnits(screenRect / res, auPerDevPixel);
 
   // Expand it for the low-res buffer if needed
@@ -988,11 +1043,25 @@ GetDisplayPortImpl(nsIContent* aContent, nsRect *aResult, float aMultiplier)
   NS_ASSERTION((rectData == nullptr) != (marginsData == nullptr),
                "Only one of rectData or marginsData should be set!");
 
+  nsRect result;
   if (rectData) {
-    *aResult = GetDisplayPortFromRectData(aContent, rectData, aMultiplier);
+    result = GetDisplayPortFromRectData(aContent, rectData, aMultiplier);
   } else {
-    *aResult = GetDisplayPortFromMarginsData(aContent, marginsData, aMultiplier);
+    result = GetDisplayPortFromMarginsData(aContent, marginsData, aMultiplier);
   }
+
+  if (!gfxPrefs::LayersTilesEnabled()) {
+    // Either we should have gotten a valid rect directly from the displayport
+    // base, or we should have computed a valid rect from the margins.
+    NS_ASSERTION(GetMaxDisplayPortSize(aContent) <= 0 ||
+                 result.width < GetMaxDisplayPortSize(aContent),
+                 "Displayport must be a valid texture size");
+    NS_ASSERTION(GetMaxDisplayPortSize(aContent) <= 0 ||
+                 result.height < GetMaxDisplayPortSize(aContent),
+                 "Displayport must be a valid texture size");
+  }
+
+  *aResult = result;
   return true;
 }