diff --git a/mozilla/layout/base/nsCSSFrameConstructor.cpp b/mozilla/layout/base/nsCSSFrameConstructor.cpp
index 5f31671ea29..f885449fdeb 100644
--- a/mozilla/layout/base/nsCSSFrameConstructor.cpp
+++ b/mozilla/layout/base/nsCSSFrameConstructor.cpp
@@ -5274,6 +5274,8 @@ nsCSSFrameConstructor::ConstructMathMLFrame(nsIPresShell*            aPresShell,
      rv = NS_NewMathMLmphantomFrame(aPresShell, &newFrame);
   else if (aTag == nsMathMLAtoms::mpadded_)
      rv = NS_NewMathMLmpaddedFrame(aPresShell, &newFrame);
+  else if (aTag == nsMathMLAtoms::mspace_)
+     rv = NS_NewMathMLmspaceFrame(aPresShell, &newFrame);
   else if (aTag == nsMathMLAtoms::mfenced_)
      rv = NS_NewMathMLmfencedFrame(aPresShell, &newFrame);
   else if (aTag == nsMathMLAtoms::mmultiscripts_)
diff --git a/mozilla/layout/html/style/src/nsCSSFrameConstructor.cpp b/mozilla/layout/html/style/src/nsCSSFrameConstructor.cpp
index 5f31671ea29..f885449fdeb 100644
--- a/mozilla/layout/html/style/src/nsCSSFrameConstructor.cpp
+++ b/mozilla/layout/html/style/src/nsCSSFrameConstructor.cpp
@@ -5274,6 +5274,8 @@ nsCSSFrameConstructor::ConstructMathMLFrame(nsIPresShell*            aPresShell,
      rv = NS_NewMathMLmphantomFrame(aPresShell, &newFrame);
   else if (aTag == nsMathMLAtoms::mpadded_)
      rv = NS_NewMathMLmpaddedFrame(aPresShell, &newFrame);
+  else if (aTag == nsMathMLAtoms::mspace_)
+     rv = NS_NewMathMLmspaceFrame(aPresShell, &newFrame);
   else if (aTag == nsMathMLAtoms::mfenced_)
      rv = NS_NewMathMLmfencedFrame(aPresShell, &newFrame);
   else if (aTag == nsMathMLAtoms::mmultiscripts_)