diff --git a/layout/base/public/nsIFrame.h b/layout/base/public/nsIFrame.h
index c89f8e240765..422f5c0fddd0 100644
--- a/layout/base/public/nsIFrame.h
+++ b/layout/base/public/nsIFrame.h
@@ -79,6 +79,10 @@ struct nsReflowMetrics {
     maxElementSize = aMaxElementSize;
     posTopMargin = 0;
     posBottomMargin = 0;
+    width = 0;
+    height = 0;
+    ascent = 0;
+    descent = 0;
   }
 };
 
diff --git a/layout/generic/nsIFrame.h b/layout/generic/nsIFrame.h
index c89f8e240765..422f5c0fddd0 100644
--- a/layout/generic/nsIFrame.h
+++ b/layout/generic/nsIFrame.h
@@ -79,6 +79,10 @@ struct nsReflowMetrics {
     maxElementSize = aMaxElementSize;
     posTopMargin = 0;
     posBottomMargin = 0;
+    width = 0;
+    height = 0;
+    ascent = 0;
+    descent = 0;
   }
 };