diff --git a/layout/generic/nsLineLayout.cpp b/layout/generic/nsLineLayout.cpp
index 7d1c0cc79aa..2ff1a7169db 100644
--- a/layout/generic/nsLineLayout.cpp
+++ b/layout/generic/nsLineLayout.cpp
@@ -743,14 +743,6 @@ nsLineLayout::ReflowFrame(nsIFrame* aFrame,
   printf("\n");
 #endif
 
-  // See if this frame depends on the width of its containing block.  If
-  // so, disable resize reflow optimizations for the line.  (Note that,
-  // to be conservative, we do this if we *try* to fit a frame on a
-  // line, even if we don't succeed.)
-  if (GetFlag(LL_GOTLINEBOX) && IsPercentageAware(aFrame)) {
-    mLineBox->DisableResizeReflowOptimization();
-  }
-
   mTextJustificationNumSpaces = 0;
   mTextJustificationNumLetters = 0;
 
@@ -824,6 +816,17 @@ nsLineLayout::ReflowFrame(nsIFrame* aFrame,
     // so no need to propagate NS_FRAME_IS_DIRTY from the parent.
   }
 
+  // See if this frame depends on the width of its containing block.  If
+  // so, disable resize reflow optimizations for the line.  (Note that,
+  // to be conservative, we do this if we *try* to fit a frame on a
+  // line, even if we don't succeed.)  (Note also that we can only make
+  // this IsPercentageAware check *after* we've constructed our
+  // nsHTMLReflowState, because that construction may be what forces aFrame
+  // to lazily initialize its (possibly-percent-valued) intrinsic size.)
+  if (GetFlag(LL_GOTLINEBOX) && IsPercentageAware(aFrame)) {
+    mLineBox->DisableResizeReflowOptimization();
+  }
+
   // Let frame know that are reflowing it. Note that we don't bother
   // positioning the frame yet, because we're probably going to end up
   // moving it when we do the vertical alignment
diff --git a/layout/reftests/svg/as-image/reftest.list b/layout/reftests/svg/as-image/reftest.list
index f859257a531..6e1766d3e3d 100644
--- a/layout/reftests/svg/as-image/reftest.list
+++ b/layout/reftests/svg/as-image/reftest.list
@@ -58,7 +58,7 @@ asserts(72) == img-and-image-1.html img-and-image-1-ref.svg
 # More complex <img> tests
 random-if(gtk2Widget) == img-anim-1.html  lime100x100-ref.html # bug 612214
 == img-content-outside-viewBox-1.html img-content-outside-viewBox-1-ref.html
-random == img-dyn-1.html img-dyn-1-ref.html # Bug 596478
+== img-dyn-1.html img-dyn-1-ref.html
 
 fails-if(d2d) == img-widthAndHeight-meet-1.html  img-widthAndHeight-meet-1-ref.html # bug 633072
 == img-widthAndHeight-meet-2.html  img-widthAndHeight-meet-2-ref.html