1 files changed, 5 insertions, 2 deletions
diff --git a/scanner.l b/scanner.l
index 9c6317ec..bb05f645 100644
--- a/scanner.l
+++ b/scanner.l
@@ -65,9 +65,12 @@
 
 #ifdef _WIN32
   /*
-   * Suppress the #include of unistd.h; Windows doesn't have it.
+   * Make sure we suppress the #include of unistd.h; Windows doesn't have
+   * unistd.h.
    */
-  #define YY_NO_UNISTD_H
+  #ifndef YY_NO_UNISTD_H
+    #define YY_NO_UNISTD_H
+  #endif
 
   #include <pcap-stdinc.h>
 #else