--- a/layout/generic/ReflowInput.cpp
+++ b/layout/generic/ReflowInput.cpp
@@ -146,35 +146,24 @@ FontSizeInflationListMarginAdjustment(co
       }
 
     }
   }
 
   return 0;
 }
 
-// NOTE: If we ever want to use SizeComputationInput for a flex item or a
-// grid item, we need to make it take the containing-block block-size as
-// well as the inline-size, since flex items and grid items resolve
-// block-direction percent margins and padding against the
-// containing-block block-size, rather than its inline-size.
 SizeComputationInput::SizeComputationInput(nsIFrame *aFrame,
                                    nsRenderingContext *aRenderingContext,
                                    WritingMode aContainingBlockWritingMode,
                                    nscoord aContainingBlockISize)
   : mFrame(aFrame)
   , mRenderingContext(aRenderingContext)
   , mWritingMode(aFrame->GetWritingMode())
 {
-  MOZ_ASSERT(!aFrame->IsFlexOrGridItem(),
-             "We're about to resolve percent margin & padding "
-             "values against CB inline size, which is incorrect for "
-             "flex/grid items. "
-             "Additionally for grid items, this path doesn't handle baseline "
-             "padding contribution - see SizeComputationInput::InitOffsets");
   ReflowInputFlags flags;
   InitOffsets(aContainingBlockWritingMode, aContainingBlockISize,
               mFrame->GetType(), flags);
 }
 
 // Initialize a reflow state for a child frame's reflow. Some state
 // is copied from the parent reflow state; the remaining state is
 // computed.