diff --git a/layout/generic/nsFontInflationData.cpp b/layout/generic/nsFontInflationData.cpp
index 58ee4c14660a..2b63fdd37583 100644
--- a/layout/generic/nsFontInflationData.cpp
+++ b/layout/generic/nsFontInflationData.cpp
@@ -38,7 +38,7 @@ nsFontInflationData::FindFontInflationDataFor(const nsIFrame *aFrame)
              bfc->Properties().Get(FontInflationDataProperty()));
 }
 
-/* static */ void
+/* static */ bool
 nsFontInflationData::UpdateFontInflationDataWidthFor(const nsHTMLReflowState& aReflowState)
 {
   nsIFrame *bfc = aReflowState.frame;
@@ -47,12 +47,22 @@ nsFontInflationData::UpdateFontInflationDataWidthFor(const nsHTMLReflowState& aR
   FrameProperties bfcProps(bfc->Properties());
   nsFontInflationData *data = static_cast<nsFontInflationData*>(
                                 bfcProps.Get(FontInflationDataProperty()));
-  if (!data) {
+  bool oldInflationEnabled;
+  nscoord oldNCAWidth;
+  if (data) {
+    oldNCAWidth = data->mNCAWidth;
+    oldInflationEnabled = data->mInflationEnabled;
+  } else {
     data = new nsFontInflationData(bfc);
     bfcProps.Set(FontInflationDataProperty(), data);
+    oldNCAWidth = -1;
+    oldInflationEnabled = true; /* not relevant */
   }
 
   data->UpdateWidth(aReflowState);
+
+  return oldNCAWidth != data->mNCAWidth ||
+         oldInflationEnabled != data->mInflationEnabled;
 }
 
 /* static */ void
diff --git a/layout/generic/nsFontInflationData.h b/layout/generic/nsFontInflationData.h
index 7e89a369ccb1..b7378d93da92 100644
--- a/layout/generic/nsFontInflationData.h
+++ b/layout/generic/nsFontInflationData.h
@@ -20,7 +20,9 @@ public:
 
   static nsFontInflationData* FindFontInflationDataFor(const nsIFrame *aFrame);
 
-  static void
+  // Returns whether the effective width changed (which requires the
+  // caller to mark its descendants dirty
+  static bool
     UpdateFontInflationDataWidthFor(const nsHTMLReflowState& aReflowState);
 
   static void MarkFontInflationDataTextDirty(nsIFrame *aFrame);
diff --git a/layout/generic/nsHTMLReflowState.cpp b/layout/generic/nsHTMLReflowState.cpp
index d4909c2db9f7..18359a669283 100644
--- a/layout/generic/nsHTMLReflowState.cpp
+++ b/layout/generic/nsHTMLReflowState.cpp
@@ -305,12 +305,6 @@ nsHTMLReflowState::Init(nsPresContext* aPresContext,
                    "have unconstrained width; this should only result from "
                    "very large sizes, not attempts at intrinsic width "
                    "calculation");
-
-  if (frame->GetStateBits() & NS_FRAME_FONT_INFLATION_FLOW_ROOT) {
-    // Create our font inflation data if we don't have it already, and
-    // give it our current width information.
-    nsFontInflationData::UpdateFontInflationDataWidthFor(*this);
-  }
 }
 
 void nsHTMLReflowState::InitCBReflowState()
@@ -364,6 +358,20 @@ IsQuirkContainingBlockHeight(const nsHTMLReflowState* rs, nsIAtom* aFrameType)
 void
 nsHTMLReflowState::InitResizeFlags(nsPresContext* aPresContext, nsIAtom* aFrameType)
 {
+  if (frame->GetStateBits() & NS_FRAME_FONT_INFLATION_FLOW_ROOT) {
+    // Create our font inflation data if we don't have it already, and
+    // give it our current width information.
+    bool dirty = nsFontInflationData::UpdateFontInflationDataWidthFor(*this);
+    if (dirty) {
+      // FIXME: This isn't so great for the cases where
+      // nsHTMLReflowState::SetComputedWith is called, if the first time
+      // we go through InitResizeFlags we set mHResize to true, and then
+      // the second time we'd set it to false even without the
+      // NS_FRAME_IS_DIRTY bit already set.
+      frame->AddStateBits(NS_FRAME_IS_DIRTY);
+    }
+  }
+
   mFlags.mHResize = !(frame->GetStateBits() & NS_FRAME_IS_DIRTY) &&
                     frame->GetSize().width !=
                       mComputedWidth + mComputedBorderPadding.LeftRight();