diff --git a/layout/base/nsPresContext.cpp b/layout/base/nsPresContext.cpp
index 543465cbea..38dc63e1f5 100644
--- a/layout/base/nsPresContext.cpp
+++ b/layout/base/nsPresContext.cpp
@@ -1733,6 +1733,9 @@ nsPresContext::SysColorChangedInternal()
     sLookAndFeelChanged = false;
   }
 
+  // Invalidate cached '-moz-windows-accent-color-applies' media query:
+  nsCSSRuleProcessor::FreeSystemMetrics();
+
   // Reset default background and foreground colors for the document since
   // they may be using system colors
   GetDocumentColorPreferences();