diff --git a/src/d_clisrv.c b/src/d_clisrv.c
index 787ff3d9e..c8092b151 100644
--- a/src/d_clisrv.c
+++ b/src/d_clisrv.c
@@ -219,31 +219,6 @@ consvar_t cv_httpsource = CVAR_INIT ("http_source", "", CV_SAVE, NULL, NULL);
 
 consvar_t cv_kicktime = CVAR_INIT ("kicktime", "10", CV_SAVE, CV_Unsigned, NULL);
 
-// https://github.com/jameds/holepunch/blob/master/holepunch.c#L75
-static int IsExternalAddress (const void *p)
-{
-	const int a = ((const unsigned char*)p)[0];
-	const int b = ((const unsigned char*)p)[1];
-
-	if (*(const int*)p == ~0)/* 255.255.255.255 */
-		return 0;
-
-	switch (a)
-	{
-		case 0:
-		case 10:
-		case 127:
-			return 0;
-		case 172:
-			return (b & ~15) != 16;/* 16 - 31 */
-		case 192:
-			return b != 168;
-		default:
-			return 1;
-	}
-}
-
-
 // Generate a message for an authenticating client to sign, with some guarantees about who we are.
 void GenerateChallenge(uint8_t *buf)
 {
@@ -292,7 +267,7 @@ shouldsign_t ShouldSignChallenge(uint8_t *message)
 	if ((max(now, then) - min(now, then)) > 60*5)
 		return SIGN_BADTIME;
 
-	if (realIP != claimedIP && IsExternalAddress(&realIP))
+	if (realIP != claimedIP && I_IsExternalAddress(&realIP))
 		return SIGN_BADIP;
 
 	return SIGN_OK;
diff --git a/src/d_net.c b/src/d_net.c
index effc48eb3..917b181fe 100644
--- a/src/d_net.c
+++ b/src/d_net.c
@@ -93,6 +93,7 @@ boolean (*I_SetBanAddress) (const char *address, const char *mask) = NULL;
 boolean (*I_SetBanUsername) (const char *username) = NULL;
 boolean (*I_SetBanReason) (const char *reason) = NULL;
 boolean (*I_SetUnbanTime) (time_t timestamp) = NULL;
+boolean (*I_IsExternalAddress) (const void *p) = NULL;
 bannednode_t *bannednode = NULL;
 
 
diff --git a/src/i_net.h b/src/i_net.h
index 9433b89fb..5755f6169 100644
--- a/src/i_net.h
+++ b/src/i_net.h
@@ -176,6 +176,7 @@ extern boolean (*I_SetBanAddress) (const char *address,const char *mask);
 extern boolean (*I_SetBanUsername) (const char *username);
 extern boolean (*I_SetBanReason) (const char *reason);
 extern boolean (*I_SetUnbanTime) (time_t timestamp);
+extern boolean (*I_IsExternalAddress) (const void *p);
 
 struct bannednode_t
 {
diff --git a/src/i_tcp.c b/src/i_tcp.c
index eb4521928..18e79fbd6 100644
--- a/src/i_tcp.c
+++ b/src/i_tcp.c
@@ -1522,6 +1522,31 @@ static void SOCK_ClearBans(void)
 	banned = NULL;
 }
 
+// https://github.com/jameds/holepunch/blob/master/holepunch.c#L75
+static int SOCK_IsExternalAddress (const void *p)
+{
+	const int a = ((const unsigned char*)p)[0];
+	const int b = ((const unsigned char*)p)[1];
+
+	if (*(const UINT32*)p == (UINT32)~0)/* 255.255.255.255 */
+		return 0;
+
+	switch (a)
+	{
+		case 0:
+		case 10:
+		case 127:
+			return 0;
+		case 172:
+			return (b & ~15) != 16;/* 16 - 31 */
+		case 192:
+			return b != 168;
+		default:
+			return 1;
+	}
+}
+
+
 boolean I_InitTcpNetwork(void)
 {
 	char serverhostname[255];
@@ -1622,6 +1647,8 @@ boolean I_InitTcpNetwork(void)
 	I_SetBanUsername = SOCK_SetBanUsername;
 	I_SetBanReason = SOCK_SetBanReason;
 	I_SetUnbanTime = SOCK_SetUnbanTime;
+	I_IsExternalAddress = SOCK_IsExternalAddress;
+
 	bannednode = SOCK_bannednode;
 
 	return ret;