diff --git a/src/goodbyedpi.c b/src/goodbyedpi.c
index 6689b71..322a783 100644
--- a/src/goodbyedpi.c
+++ b/src/goodbyedpi.c
@@ -181,7 +181,11 @@ static void add_filter_str(int proto, int port) {
     const char *udp = " or (udp and !impostor and !loopback and (udp.SrcPort == %d or udp.DstPort == %d))";
     const char *tcp = " or (tcp and !impostor and !loopback " MAXPAYLOADSIZE_TEMPLATE " and (tcp.SrcPort == %d or tcp.DstPort == %d))";
 
-    size_t new_filter_size = strlen(filter_string) + (proto == IPPROTO_UDP ? strlen(udp) : strlen(tcp)) + 16;
+    const size_t udp_length = strlen(udp);
+    const size_t tcp_length = strlen(tcp);
+    const size_t filter_string_length = strlen(filter_string);
+
+    size_t new_filter_size = filter_string_length + (proto == IPPROTO_UDP ? udp_length : tcp_length) + 16;
     char *new_filter = malloc(new_filter_size);
 
     sprintf(new_filter, proto == IPPROTO_UDP ? udp : tcp, port, port);
@@ -190,11 +194,10 @@ static void add_filter_str(int proto, int port) {
     filter_string = new_filter;
 }
 
-static void add_ip_id_str(int id) {
-    const char *ipid = " or ip.Id == %d";
-    char *addfilter = malloc(strlen(ipid) + 16);
 
-    sprintf(addfilter, ipid, id);
+static void add_ip_id_str(int id) {
+    char addfilter[32];
+    snprintf(addfilter, sizeof(addfilter), " or ip.Id == %d", id);
 
     char *newstr = repl_str(filter_string, IPID_TEMPLATE, addfilter);
     free(filter_string);
@@ -205,17 +208,20 @@ static void add_ip_id_str(int id) {
     filter_passive_string = newstr;
 }
 
+
 static void add_maxpayloadsize_str(unsigned short maxpayload) {
     const char *maxpayloadsize_str = "and (tcp.PayloadLength ? tcp.PayloadLength < %hu or tcp.Payload32[0] == 0x47455420 or tcp.Payload32[0] == 0x504F5354 : true)";
-    char *addfilter = malloc(strlen(maxpayloadsize_str) + 16);
+    char *addfilter;
 
-    sprintf(addfilter, maxpayloadsize_str, maxpayload);
+    asprintf(&addfilter, maxpayloadsize_str, maxpayload);
 
     char *newstr = repl_str(filter_string, MAXPAYLOADSIZE_TEMPLATE, addfilter);
     free(filter_string);
     filter_string = newstr;
+    free(addfilter);
 }
 
+
 static void finalize_filter_strings() {
     char *newstr = repl_str(filter_string, IPID_TEMPLATE, "");
     free(filter_string);