diff --git a/src/arg_cmd.c b/src/arg_cmd.c
index 6fcd5db..1141b57 100644
--- a/src/arg_cmd.c
+++ b/src/arg_cmd.c
@@ -61,7 +61,7 @@ void arg_set_module_name(const char* name) {
 #if (defined(__STDC_LIB_EXT1__) && defined(__STDC_WANT_LIB_EXT1__)) || (defined(__STDC_SECURE_LIB__) && defined(__STDC_WANT_SECURE_LIB__))
     strncpy_s(s_module_name, slen + 1, name, slen);
 #else
-    strncpy(s_module_name, name, slen);
+    memcpy(s_module_name, name, slen);
 #endif
 }
 
@@ -81,7 +81,7 @@ void arg_set_module_version(int major, int minor, int patch, const char* tag) {
 #if (defined(__STDC_LIB_EXT1__) && defined(__STDC_WANT_LIB_EXT1__)) || (defined(__STDC_SECURE_LIB__) && defined(__STDC_WANT_SECURE_LIB__))
     strncpy_s(s_mod_ver_tag, slen_tag + 1, tag, slen_tag);
 #else
-    strncpy(s_mod_ver_tag, tag, slen_tag);
+    memcpy(s_mod_ver_tag, tag, slen_tag);
 #endif
 
     ds = arg_dstr_create();
@@ -98,7 +98,7 @@ void arg_set_module_version(int major, int minor, int patch, const char* tag) {
 #if (defined(__STDC_LIB_EXT1__) && defined(__STDC_WANT_LIB_EXT1__)) || (defined(__STDC_SECURE_LIB__) && defined(__STDC_WANT_SECURE_LIB__))
     strncpy_s(s_mod_ver, slen_ds + 1, arg_dstr_cstr(ds), slen_ds);
 #else
-    strncpy(s_mod_ver, arg_dstr_cstr(ds), slen_ds);
+    memcpy(s_mod_ver, arg_dstr_cstr(ds), slen_ds);
 #endif
 
     arg_dstr_destroy(ds);
@@ -153,8 +153,8 @@ void arg_cmd_register(const char* name, arg_cmdfn* proc, const char* description
     strncpy_s(cmd_info->name, ARG_CMD_NAME_LEN, name, strlen(name));
     strncpy_s(cmd_info->description, ARG_CMD_DESCRIPTION_LEN, description, strlen(description));
 #else
-    strncpy(cmd_info->name, name, strlen(name));
-    strncpy(cmd_info->description, description, strlen(description));
+    memcpy(cmd_info->name, name, strlen(name));
+    memcpy(cmd_info->description, description, strlen(description));
 #endif
 
     cmd_info->proc = proc;
@@ -166,7 +166,7 @@ void arg_cmd_register(const char* name, arg_cmdfn* proc, const char* description
 #if (defined(__STDC_LIB_EXT1__) && defined(__STDC_WANT_LIB_EXT1__)) || (defined(__STDC_SECURE_LIB__) && defined(__STDC_WANT_SECURE_LIB__))
     strncpy_s((char*)k, slen_name + 1, name, slen_name);
 #else
-    strncpy((char*)k, name, slen_name);
+    memcpy((char*)k, name, slen_name);
 #endif
 
     arg_hashtable_insert(s_hashtable, k, cmd_info);
diff --git a/src/arg_dstr.c b/src/arg_dstr.c
index 76e7a92..884db66 100644
--- a/src/arg_dstr.c
+++ b/src/arg_dstr.c
@@ -174,12 +174,12 @@ char* arg_dstr_cstr(arg_dstr_t ds) /* Interpreter whose result to return. */
 
 void arg_dstr_cat(arg_dstr_t ds, const char* str) {
     setup_append_buf(ds, (int)strlen(str) + 1);
-    strncat(ds->data, str, strlen(str));
+    memcpy(ds->data + strlen(ds->data), str, strlen(str));
 }
 
 void arg_dstr_catc(arg_dstr_t ds, char c) {
     setup_append_buf(ds, 2);
-    strncat(ds->data, &c, 1);
+    memcpy(ds->data + strlen(ds->data), &c, 1);
 }
 
 /*
@@ -296,6 +296,7 @@ static void setup_append_buf(arg_dstr_t ds, int new_space) {
             total_space *= 2;
         }
         newbuf = (char*)xmalloc((unsigned)total_space);
+        memset(newbuf, 0, total_space);
         strcpy(newbuf, ds->data);
         if (ds->append_data != NULL) {
             xfree(ds->append_data);