diff --git a/tools/pnnx/src/main.cpp b/tools/pnnx/src/main.cpp
index 69a0c9ffd..d040508e1 100644
--- a/tools/pnnx/src/main.cpp
+++ b/tools/pnnx/src/main.cpp
@@ -163,8 +163,9 @@ static bool file_maybe_numpy(const std::string& path)
         return false;
     }
     
-    char signature[6];
+    char signature[7];
     fread(signature, sizeof(char), 6, fp);
+    signature[6] = '\0';
 
     fclose(fp);
 
@@ -180,7 +181,7 @@ static void prase_numpy_file_list(char* s, std::vector<std::vector<int64_t> >& s
     {
         if (!file_maybe_numpy(s))
         {
-            fprintf(stderr, "%s is not a vaild numpy file", s);
+            fprintf(stderr, "%s is not a vaild numpy file", s.c_str());
             return ;
         }
         pnnx::prase_numpy_file(s.c_str(), shapes, types, contents);
diff --git a/tools/pnnx/src/utils.cpp b/tools/pnnx/src/utils.cpp
index 6824fc7f8..ba860fc65 100644
--- a/tools/pnnx/src/utils.cpp
+++ b/tools/pnnx/src/utils.cpp
@@ -4,6 +4,7 @@
 #include "utils.h"
 
 #include <stdio.h>
+#include <stdint.h>
 #include <string.h>
 #include <math.h>
 
@@ -151,7 +152,8 @@ void prase_dtype(char* dtype, std::vector<std::string>& types, char& endian)
     std::string s;
     s += dtype[0];
     char p[10];
-    s += itoa(8 * atoi(dtype + 1), p, 10);
+    sprintf(p, "%d", 8 * atoi(dtype + 1));
+    s += p;
     types.push_back(s);
 }
 
@@ -284,7 +286,7 @@ void prase_numpy_file(const char * path,
         fclose(fp);
         return ;
     }
-    
+
     char magic[6];
     fread(magic, sizeof(char), 6, fp);