diff --git a/xpcom/glue/nsHashKeys.h b/xpcom/glue/nsHashKeys.h
index 8336fe12b61..c50b1f075c9 100644
--- a/xpcom/glue/nsHashKeys.h
+++ b/xpcom/glue/nsHashKeys.h
@@ -52,6 +52,7 @@
 #endif
 
 #include <stdlib.h>
+#include <string.h>
 
 /** @file nsHashKeys.h
  * standard HashKey classes for nsBaseHashtable and relatives. Each of these