diff --git a/TAP.c b/TAP.c
index 6dbd37b..50fdbc4 100644
--- a/TAP.c
+++ b/TAP.c
@@ -14,6 +14,7 @@ extern int device_type;
 extern char if_name[IFNAMSIZ];
 extern char* ipv4_addr;
 extern char* ipv6_addr;
+extern long ipv6_prefixLen;
 extern char* netmask;
 extern void cleanup();
 
@@ -259,23 +260,6 @@ int open_tap(void) {
                                         exit(1);
                                     }
 
-                                    char* ipPart = strtok(ipv6_addr, "/");
-                                    char* prefixPart_s = strtok(NULL, "/");
-                                    printf("ip part: %s\n", ipPart);
-
-                                    if(!prefixPart_s)
-                                    {
-                                        printf("No prefix length was provided\n"); // TODO: Move logic into arg parsing
-                                        close(inet6);
-                                        cleanup();
-                                        exit(1);
-                                    }
-                                    printf("prefix part: %s\n", prefixPart_s);
-
-                                    long prefixLen_l = strtol(prefixPart_s, NULL, 10); // TODO: Add handling here for errors (using errno)
-
-
-
                                     // Convert ASCII IPv6 address to ABI structure
                                     struct in6_addr six_addr_itself;
                                     memset(&six_addr_itself, 0, sizeof(struct in6_addr));
@@ -288,7 +272,7 @@ int open_tap(void) {
                                     }
 
                                     // Add user's requested address
-                                    trySixSet(ifr.ifr_ifindex, six_addr_itself, prefixLen_l);
+                                    trySixSet(ifr.ifr_ifindex, six_addr_itself, ipv6_prefixLen);
 
                                     close(inet6);
                                 }
diff --git a/tncattach.c b/tncattach.c
index da3cdfa..6aa12f1 100644
--- a/tncattach.c
+++ b/tncattach.c
@@ -41,6 +41,7 @@ char* ipv4_addr;
 char* netmask;
 
 char* ipv6_addr;
+long ipv6_prefixLen;
 
 char* tcp_host;
 int tcp_port;
@@ -488,13 +489,32 @@ static error_t parse_opt(int key, char *arg, struct argp_state *state) {
                 perror("Sorry, but you had noipv6 set yet want to use ipv6?\n");
                 exit(EXIT_FAILURE);
             }
-            arguments->ipv6 = arg;
+
+            char* ipPart_s = strtok(arg, "/");
+            char* prefixPart_s = strtok(NULL, "/");
+            printf("ipPart_s: %s\n", ipPart_s);
+
+            if(!prefixPart_s)
+            {
+                printf("No prefix length was provided\n");
+                exit(1);
+            }
+            printf("prefixPart_s: %s\n", prefixPart_s);
+
+            long prefixLen_l = strtol(prefixPart_s, NULL, 10); // TODO: Add handling here for errors (using errno)
+
+
+            arguments->ipv6 = ipPart_s;
+            
             arguments->set_ipv6 = true;
 
-            // Save to the global for other modules to access it
+            // Copy across global IPv6 address
             ipv6_addr = malloc(strlen(arguments->ipv6)+1);
             strcpy(ipv6_addr, arguments->ipv6);
 
+            // Set global IPv6 prefix length
+            ipv6_prefixLen = prefixLen_l;
+
             printf("MTU was %d, setting to minimum of %d as is required for IPv6\n", arguments->mtu, 1280);
             arguments->mtu = 1280;
             break;