diff --git a/src/goodbyedpi.c b/src/goodbyedpi.c
index ade82080..c3f8def2 100644
--- a/src/goodbyedpi.c
+++ b/src/goodbyedpi.c
@@ -185,17 +185,14 @@ static void add_filter_str(int proto, int port) {
     const char *tcp = " or (tcp and !impostor and !loopback " MAXPAYLOADSIZE_TEMPLATE " and " \
                       "(tcp.SrcPort == %d or tcp.DstPort == %d))";
 
-    char *current_filter = filter_string;
-    size_t current_filter_length = strlen(current_filter);
-    size_t new_filter_size = current_filter_length +
-            (proto == IPPROTO_UDP ? strlen(udp) : strlen(tcp)) + 16;
-    char *new_filter = malloc(new_filter_size);
+    const char *template = proto == IPPROTO_UDP ? udp : tcp;
+    size_t needed_size = strlen(filter_string) + strlen(template) + 16;
 
-    snprintf(new_filter, new_filter_size, "%s%s", current_filter, 
-             proto == IPPROTO_UDP ? udp : tcp, port, port);
+    if (needed_size > strlen(filter_string)) {
+        filter_string = realloc(filter_string, needed_size);
+    }
 
-    filter_string = new_filter;
-    free(current_filter);
+    snprintf(filter_string + strlen(filter_string), needed_size, template, port, port);
 }
 
 static void add_ip_id_str(int id) {
@@ -224,7 +221,6 @@ static void add_maxpayloadsize_str(unsigned short maxpayload) {
     free(addfilter);
 }
 
-
 static void finalize_filter_strings() {
     char *newstr = repl_str(filter_string, IPID_TEMPLATE, "");
     free(filter_string);
@@ -238,17 +234,13 @@ static void finalize_filter_strings() {
 static const char* dumb_memmem(const char* haystack, unsigned int hlen,
                                const char* needle, unsigned int nlen)
 {
-    // naive implementation
+    if (nlen == 0) return haystack;
+
     if (nlen > hlen) return NULL;
-    size_t i;
-    for (i=0; i<hlen-nlen+1; i++) {
-        if (memcmp(haystack+i,needle,nlen)==0) {
-            return haystack+i;
-        }
-    }
-    return NULL;
+    return strstr(haystack, needle);
 }
 
+
 unsigned short int atousi(const char *str, const char *msg) {
     long unsigned int res = strtoul(str, NULL, 10u);
     enum {