diff --git a/layout/mathml/nsMathMLmtableFrame.cpp b/layout/mathml/nsMathMLmtableFrame.cpp
index 5f522c706054..a63b8464b8fa 100644
--- a/layout/mathml/nsMathMLmtableFrame.cpp
+++ b/layout/mathml/nsMathMLmtableFrame.cpp
@@ -226,7 +226,7 @@ ApplyBorderToStyle(const nsMathMLmtdFrame* aFrame,
 }
 
 static nsMargin
-ComputeBorderOverflow(nsMathMLmtdFrame* aFrame, nsStyleBorder aStyleBorder)
+ComputeBorderOverflow(nsMathMLmtdFrame* aFrame, const nsStyleBorder& aStyleBorder)
 {
   nsMargin overflow;
   int32_t rowIndex;