diff --git a/examples/pack.c b/examples/pack.c
index 8be2349..5144eae 100644
--- a/examples/pack.c
+++ b/examples/pack.c
@@ -13,11 +13,13 @@ int main(int argc, char **argv) {
 
     if ((len = skipstone_message_pack(buf,
                                       SKIPSTONE_MESSAGE_MAX_PAYLOAD,
-                                      "CCCC",
+                                      "CCCCzz",
                                       1,
                                       2,
                                       3,
-                                      4)) < 0) {
+                                      4,
+                                      "KMFDM",
+                                      "Nihil")) < 0) {
         fprintf(stderr, "%s: %s: %s\n", argv[0],
             "skipstone_message_pack()", strerror(errno));
 
diff --git a/include/skipstone/message.h b/include/skipstone/message.h
index e370c8c..63b56e2 100644
--- a/include/skipstone/message.h
+++ b/include/skipstone/message.h
@@ -8,6 +8,7 @@
 #include <skipstone/map.h>
 
 #define SKIPSTONE_MESSAGE_MAX_PAYLOAD 4096
+#define SKIPSTONE_MESSAGE_MAX_STRLEN   256
 
 ssize_t skipstone_message_pack(void *message,
                                size_t len,
diff --git a/src/message.c b/src/message.c
index 632618a..04a5dbb 100644
--- a/src/message.c
+++ b/src/message.c
@@ -60,10 +60,16 @@ ssize_t skipstone_message_pack(void *message,
                 char *value = va_arg(args, char *);
                 size_t sz = strlen(value);
 
-                if (len < offset + sz) {
+                if (len < offset + sz + 1) {
                     goto done;
+                } else if (sz > SKIPSTONE_MESSAGE_MAX_STRLEN) {
+                    errno = EOVERFLOW;
+
+                    goto error_toobig;
                 }
 
+                ((uint8_t *)message)[offset++] = (uint8_t)sz;
+
                 memcpy((uint8_t *)message + offset, value, sz);
 
                 offset += sz;
@@ -83,6 +89,7 @@ ssize_t skipstone_message_pack(void *message,
 done:
     return offset;
 
+error_toobig:
 error_invalid_template:
     return -1;
 }