diff --git a/gfx/2d/DrawTargetCairo.cpp b/gfx/2d/DrawTargetCairo.cpp
index b44e57c93ea..578684df26b 100644
--- a/gfx/2d/DrawTargetCairo.cpp
+++ b/gfx/2d/DrawTargetCairo.cpp
@@ -216,15 +216,22 @@ static cairo_surface_t* CopyToImageSurface(unsigned char* aData,
   }
 
   unsigned char* surfData = cairo_image_surface_get_data(surf);
-  int surfStride = cairo_image_surface_get_stride(surf);
-  int32_t pixelWidth = BytesPerPixel(aFormat);
+  size_t surfStride = cairo_image_surface_get_stride(surf);
+  size_t pixelWidth = BytesPerPixel(aFormat);
+  size_t rowDataWidth = size_t(aRectWidth) * pixelWidth;
+  if (rowDataWidth > surfStride || rowDataWidth > size_t(aStride)) {
+    cairo_surface_destroy(surf);
+    return nullptr;
+  }
 
-  unsigned char* source = aData + aRect.Y() * aStride + aRect.X() * pixelWidth;
+  const unsigned char* sourceRow = aData + size_t(aRect.Y()) * size_t(aStride) +
+                                   size_t(aRect.X()) * pixelWidth;
+  unsigned char* destRow = surfData;
 
-  MOZ_ASSERT(aStride >= aRectWidth * pixelWidth);
   for (int32_t y = 0; y < aRectHeight; ++y) {
-    memcpy(surfData + y * surfStride, source + y * aStride,
-           aRectWidth * pixelWidth);
+    memcpy(destRow, sourceRow, rowDataWidth);
+    sourceRow += aStride;
+    destRow += surfStride;
   }
   cairo_surface_mark_dirty(surf);
   return surf;
@@ -250,12 +257,12 @@ static cairo_surface_t* GetAsImageSurface(cairo_surface_t* aSurface) {
 static cairo_surface_t* CreateSubImageForData(unsigned char* aData,
                                               const IntRect& aRect, int aStride,
                                               SurfaceFormat aFormat) {
-  if (!aData) {
+  if (!aData || aStride < 0) {
     gfxWarning() << "DrawTargetCairo.CreateSubImageForData null aData";
     return nullptr;
   }
-  unsigned char* data =
-      aData + aRect.Y() * aStride + aRect.X() * BytesPerPixel(aFormat);
+  unsigned char* data = aData + size_t(aRect.Y()) * size_t(aStride) +
+                        size_t(aRect.X()) * size_t(BytesPerPixel(aFormat));
 
   cairo_surface_t* image = cairo_image_surface_create_for_data(
       data, GfxFormatToCairoFormat(aFormat), aRect.Width(), aRect.Height(),