diff --git a/mongoose.c b/mongoose.c
index 200e750f..3cd70896 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -6633,8 +6633,7 @@ void mg_rpc_add(struct mg_rpc **head, struct mg_str method,
                 void (*fn)(struct mg_rpc_req *), void *fn_data) {
   struct mg_rpc *rpc = (struct mg_rpc *) calloc(1, sizeof(*rpc));
   if (rpc != NULL) {
-    rpc->method.buf = mg_mprintf("%.*s", method.len, method.buf);
-    rpc->method.len = method.len;
+    rpc->method = mg_strdup(method);
     rpc->fn = fn;
     rpc->fn_data = fn_data;
     rpc->next = *head, *head = rpc;
@@ -8048,6 +8047,20 @@ int mg_casecmp(const char *s1, const char *s2) {
   return diff;
 }
 
+struct mg_str mg_strdup(const struct mg_str s) {
+  struct mg_str r = {NULL, 0};
+  if (s.len > 0 && s.buf != NULL) {
+    char *sc = (char *) calloc(1, s.len + 1);
+    if (sc != NULL) {
+      memcpy(sc, s.buf, s.len);
+      sc[s.len] = '\0';
+      r.buf = sc;
+      r.len = s.len;
+    }
+  }
+  return r;
+}
+
 int mg_strcmp(const struct mg_str str1, const struct mg_str str2) {
   size_t i = 0;
   while (i < str1.len && i < str2.len) {
@@ -10605,8 +10618,7 @@ static int mg_parse_pem(const struct mg_str pem, const struct mg_str label,
   const char *c;
   struct mg_str caps[5];
   if (!mg_match(pem, mg_str("#-----BEGIN #-----#-----END #-----#"), caps)) {
-    der->buf = mg_mprintf("%.*s", pem.len, pem.buf);
-    der->len = pem.len;
+    *der = mg_strdup(pem);
     return 0;
   }
   if (mg_strcmp(caps[1], label) != 0 || mg_strcmp(caps[3], label) != 0) {
diff --git a/mongoose.h b/mongoose.h
index 10f04be5..79f0d6e7 100644
--- a/mongoose.h
+++ b/mongoose.h
@@ -186,7 +186,7 @@ extern "C" {
 #define calloc(a, b) mg_calloc(a, b)
 #define free(a) vPortFree(a)
 #define malloc(a) pvPortMalloc(a)
-#define strdup(s) mg_mprintf("%s", s)
+#define strdup(s) ((char *) mg_strdup(mg_str(s)).buf)
 
 // Re-route calloc/free to the FreeRTOS's functions, don't use stdlib
 static inline void *mg_calloc(size_t cnt, size_t size) {
@@ -288,7 +288,7 @@ extern uint32_t rt_time_get(void);
 #include "cmsis_os2.h"  // keep this include
 #endif
 
-#define strdup(s) mg_mprintf("%s", s)
+#define strdup(s) ((char *) mg_strdup(mg_str(s)).buf)
 
 #if defined(__ARMCC_VERSION)
 #define mode_t size_t
@@ -861,6 +861,7 @@ struct mg_str mg_str_n(const char *s, size_t n);
 int mg_casecmp(const char *s1, const char *s2);
 int mg_strcmp(const struct mg_str str1, const struct mg_str str2);
 int mg_strcasecmp(const struct mg_str str1, const struct mg_str str2);
+struct mg_str mg_strdup(const struct mg_str s);
 bool mg_match(struct mg_str str, struct mg_str pattern, struct mg_str *caps);
 bool mg_span(struct mg_str s, struct mg_str *a, struct mg_str *b, char delim);
 
diff --git a/src/arch_freertos.h b/src/arch_freertos.h
index 9ad78998..e3d81bd7 100644
--- a/src/arch_freertos.h
+++ b/src/arch_freertos.h
@@ -32,7 +32,7 @@
 #define calloc(a, b) mg_calloc(a, b)
 #define free(a) vPortFree(a)
 #define malloc(a) pvPortMalloc(a)
-#define strdup(s) mg_mprintf("%s", s)
+#define strdup(s) ((char *) mg_strdup(mg_str(s)).buf)
 
 // Re-route calloc/free to the FreeRTOS's functions, don't use stdlib
 static inline void *mg_calloc(size_t cnt, size_t size) {
diff --git a/src/arch_rtx.h b/src/arch_rtx.h
index cbf79d25..a6008db7 100644
--- a/src/arch_rtx.h
+++ b/src/arch_rtx.h
@@ -22,7 +22,7 @@ extern uint32_t rt_time_get(void);
 #include "cmsis_os2.h"  // keep this include
 #endif
 
-#define strdup(s) mg_mprintf("%s", s)
+#define strdup(s) ((char *) mg_strdup(mg_str(s)).buf)
 
 #if defined(__ARMCC_VERSION)
 #define mode_t size_t
diff --git a/src/rpc.c b/src/rpc.c
index 509a2be4..9efe9671 100644
--- a/src/rpc.c
+++ b/src/rpc.c
@@ -5,8 +5,7 @@ void mg_rpc_add(struct mg_rpc **head, struct mg_str method,
                 void (*fn)(struct mg_rpc_req *), void *fn_data) {
   struct mg_rpc *rpc = (struct mg_rpc *) calloc(1, sizeof(*rpc));
   if (rpc != NULL) {
-    rpc->method.buf = mg_mprintf("%.*s", method.len, method.buf);
-    rpc->method.len = method.len;
+    rpc->method = mg_strdup(method);
     rpc->fn = fn;
     rpc->fn_data = fn_data;
     rpc->next = *head, *head = rpc;
diff --git a/src/str.c b/src/str.c
index c0edf373..cb997092 100644
--- a/src/str.c
+++ b/src/str.c
@@ -23,6 +23,20 @@ int mg_casecmp(const char *s1, const char *s2) {
   return diff;
 }
 
+struct mg_str mg_strdup(const struct mg_str s) {
+  struct mg_str r = {NULL, 0};
+  if (s.len > 0 && s.buf != NULL) {
+    char *sc = (char *) calloc(1, s.len + 1);
+    if (sc != NULL) {
+      memcpy(sc, s.buf, s.len);
+      sc[s.len] = '\0';
+      r.buf = sc;
+      r.len = s.len;
+    }
+  }
+  return r;
+}
+
 int mg_strcmp(const struct mg_str str1, const struct mg_str str2) {
   size_t i = 0;
   while (i < str1.len && i < str2.len) {
diff --git a/src/str.h b/src/str.h
index 1cb446e2..ffeded37 100644
--- a/src/str.h
+++ b/src/str.h
@@ -16,6 +16,7 @@ struct mg_str mg_str_n(const char *s, size_t n);
 int mg_casecmp(const char *s1, const char *s2);
 int mg_strcmp(const struct mg_str str1, const struct mg_str str2);
 int mg_strcasecmp(const struct mg_str str1, const struct mg_str str2);
+struct mg_str mg_strdup(const struct mg_str s);
 bool mg_match(struct mg_str str, struct mg_str pattern, struct mg_str *caps);
 bool mg_span(struct mg_str s, struct mg_str *a, struct mg_str *b, char delim);
 
diff --git a/src/tls_builtin.c b/src/tls_builtin.c
index ece5dad5..781fdb9d 100644
--- a/src/tls_builtin.c
+++ b/src/tls_builtin.c
@@ -1233,8 +1233,7 @@ static int mg_parse_pem(const struct mg_str pem, const struct mg_str label,
   const char *c;
   struct mg_str caps[5];
   if (!mg_match(pem, mg_str("#-----BEGIN #-----#-----END #-----#"), caps)) {
-    der->buf = mg_mprintf("%.*s", pem.len, pem.buf);
-    der->len = pem.len;
+    *der = mg_strdup(pem);
     return 0;
   }
   if (mg_strcmp(caps[1], label) != 0 || mg_strcmp(caps[3], label) != 0) {
diff --git a/test/unit_test.c b/test/unit_test.c
index 3691476f..8e90f706 100644
--- a/test/unit_test.c
+++ b/test/unit_test.c
@@ -1854,6 +1854,12 @@ static bool chkdbl(struct mg_str s, double val) {
 }
 
 static void test_str(void) {
+  {
+    struct mg_str s = mg_strdup(mg_str("a"));
+    ASSERT(mg_strcmp(s, mg_str("a")) == 0);
+    free((void *) s.buf);
+  }
+
   {
     const char *s;
     struct mg_str a = mg_str("hello"), b = mg_str("a"), c = mg_str(NULL);
diff --git a/tutorials/core/multi-threaded/main.c b/tutorials/core/multi-threaded/main.c
index efc439ee..6200e18e 100644
--- a/tutorials/core/multi-threaded/main.c
+++ b/tutorials/core/multi-threaded/main.c
@@ -50,8 +50,7 @@ static void fn(struct mg_connection *c, int ev, void *ev_data) {
       // Multithreading code path
       struct thread_data *data =
           (struct thread_data *) calloc(1, sizeof(*data));  // Worker owns it
-      data->message.buf = mg_mprintf("%.*s", hm->message.len, hm->message.buf);
-      data->message.len = hm->message.len;  // Pass message
+      data->message = mg_strdup(hm->message); // Pass message
       data->conn_id = c->id;
       data->mgr = c->mgr;
       start_thread(thread_function, data);  // Start thread and pass data
diff --git a/tutorials/mqtt/mqtt-server/main.c b/tutorials/mqtt/mqtt-server/main.c
index 4d32eef6..5d188c27 100644
--- a/tutorials/mqtt/mqtt-server/main.c
+++ b/tutorials/mqtt/mqtt-server/main.c
@@ -80,8 +80,7 @@ static void fn(struct mg_connection *c, int ev, void *ev_data) {
         while ((pos = mg_mqtt_next_sub(mm, &topic, &qos, pos)) > 0) {
           struct sub *sub = calloc(1, sizeof(*sub));
           sub->c = c;
-          sub->topic.buf = mg_mprintf("%.*s", topic.len, topic.buf);
-          sub->topic.len = topic.len;
+          sub->topic = mg_strdup(topic);
           sub->qos = qos;
           LIST_ADD_HEAD(struct sub, &s_subs, sub);
           MG_INFO(