diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index b006eadf78a6..9732c16fb0e5 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -882,7 +882,8 @@ GetDisplayPortFromMarginsData(nsIContent* aContent,
   if (nsRect* baseData = static_cast<nsRect*>(aContent->GetProperty(nsGkAtoms::DisplayPortBase))) {
     base = *baseData;
   } else {
-    NS_WARNING("Attempting to get a margins-based displayport with no base data!");
+    // In theory we shouldn't get here, but we do sometimes (see bug 1212136).
+    // Fall through for graceful handling.
   }
 
   nsIFrame* frame = aContent->GetPrimaryFrame();