diff --git a/mozilla/layout/forms/nsComboboxControlFrame.cpp b/mozilla/layout/forms/nsComboboxControlFrame.cpp
index cd6264f4361..4298a5dd977 100644
--- a/mozilla/layout/forms/nsComboboxControlFrame.cpp
+++ b/mozilla/layout/forms/nsComboboxControlFrame.cpp
@@ -1045,7 +1045,10 @@ nsComboboxControlFrame::SelectionChanged()
           nsCOMPtr<nsIPresShell> shell;
           rv = mPresContext->GetShell(getter_AddRefs(shell));
           if (NS_SUCCEEDED(rv) && shell) {
-            shell->AppendReflowCommand(cmd);
+            if (NS_SUCCEEDED(shell->EnterReflowLock())) {
+              shell->AppendReflowCommand(cmd);
+              shell->ExitReflowLock();
+            }
           }
           NS_RELEASE(cmd);
         }
diff --git a/mozilla/layout/html/forms/src/nsComboboxControlFrame.cpp b/mozilla/layout/html/forms/src/nsComboboxControlFrame.cpp
index cd6264f4361..4298a5dd977 100644
--- a/mozilla/layout/html/forms/src/nsComboboxControlFrame.cpp
+++ b/mozilla/layout/html/forms/src/nsComboboxControlFrame.cpp
@@ -1045,7 +1045,10 @@ nsComboboxControlFrame::SelectionChanged()
           nsCOMPtr<nsIPresShell> shell;
           rv = mPresContext->GetShell(getter_AddRefs(shell));
           if (NS_SUCCEEDED(rv) && shell) {
-            shell->AppendReflowCommand(cmd);
+            if (NS_SUCCEEDED(shell->EnterReflowLock())) {
+              shell->AppendReflowCommand(cmd);
+              shell->ExitReflowLock();
+            }
           }
           NS_RELEASE(cmd);
         }