diff --git a/configure.ac b/configure.ac
index 53bacac4..79d352a8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -431,7 +431,7 @@ dnl
       AS_IF([ test "x$withval" = xno ], [],
         AS_IF([ test "x$withval" = x -o "x$withval" = xyes ],
           [AC_MSG_ERROR([--with-iptables requires an argument specifying a path to iptables])],
-          [ IPTABLES_EXE=$withval ]
+          [ FORCE_IPTABLES_EXE=$withval ]
         )
       )
     ],
@@ -449,7 +449,7 @@ dnl
       AS_IF([ test "x$withval" = xno ], [],
         AS_IF([ test "x$withval" = x -o "x$withval" = xyes ],
           [AC_MSG_ERROR([--with-ipfw requires an argument specifying a path to ipfw])],
-          [ IPFW_EXE=$withval ]
+          [ FORCE_IPFW_EXE=$withval ]
         )
       )
     ],
@@ -467,7 +467,7 @@ dnl
       AS_IF([ test "x$withval" = xno ], [],
         AS_IF([ test "x$withval" = x -o "x$withval" = xyes ],
           [AC_MSG_ERROR([--with-pf requires an argument specifying a path to pf])],
-          [ PF_EXE=$withval ]
+          [ FORCE_PF_EXE=$withval ]
         )
       )
     ],
@@ -485,7 +485,7 @@ dnl
       AS_IF([ test "x$withval" = xno ], [],
         AS_IF([ test "x$withval" = x -o "x$withval" = xyes ],
           [AC_MSG_ERROR([--with-ipf requires an argument specifying a path to ipf])],
-          [ IPF_EXE=$withval ]
+          [ FORCE_IPF_EXE=$withval ]
         )
       )
     ],
@@ -494,6 +494,31 @@ dnl
     ]
   )
 
+dnl If a firewall was forced. set the appropriate _EXE var and clear the others.
+dnl
+  AS_IF([test "x$FORCE_IPTABLES_EXE" != x], [
+    IPTABLES_EXE="$FORCE_IPTABLES_EXE"    
+  ],[
+    AS_IF([test "x$FORCE_IPFW_EXE" != x], [
+      IPFW_EXE="$FORCE_IPFW_EXE"    
+      IPTABLES_EXE=""    
+    ],[
+      AS_IF([test "x$FORCE_PF_EXE" != x], [
+        PF_EXE="$FORCE_PF_EXE"    
+        IPFW_EXE=""    
+        IPTABLES_EXE=""    
+      ],[
+        AS_IF([test "x$FORCE_IPF_EXE" != x], [
+          IPF_EXE="$FORCE_IPF_EXE"    
+          PF_EXE=""    
+          IPFW_EXE=""    
+          IPTABLES_EXE=""    
+        ]
+      ]
+    ]
+  ]
+  ))))
+
 dnl Determine which firewall exe we use (if we have one).
 dnl If iptables was found or specified, it wins, then we fallback to ipfw,
 dnl then pf, and otherwise we try ipf.