diff --git a/sha1.cpp b/sha1.cpp
index f7fd3c4..432aeef 100644
--- a/sha1.cpp
+++ b/sha1.cpp
@@ -18,7 +18,8 @@
 /* Based on: http://www.zedwood.com/article/cpp-sha1-function
  * Modified by NewYaroslav, 2025-04-15
  */
- 
+
+#include <cstdio>
 #include <algorithm>
 #include "sha1.hpp"
 
@@ -247,7 +248,7 @@ namespace hmac_hash {
         char buf[2 * hmac_hash::SHA1::DIGEST_SIZE + 1];
         std::fill(buf, buf + (2 * hmac_hash::SHA1::DIGEST_SIZE + 1), '\0');
         for(size_t i = 0; i < hmac_hash::SHA1::DIGEST_SIZE; ++i) {
-            sprintf(buf + i * 2, "%02x", digest[i]);
+            std::snprintf(buf + i * 2, sizeof(buf) - i * 2, "%02x", digest[i]);
         }
         return std::string(buf, (2 * hmac_hash::SHA1::DIGEST_SIZE));
     }
diff --git a/sha256.cpp b/sha256.cpp
index 41bf52b..85e543b 100644
--- a/sha256.cpp
+++ b/sha256.cpp
@@ -41,6 +41,7 @@
 
 #include <algorithm>
 #include <cstring>
+#include <cstdio>
 //#include <fstream>
 #include "sha256.hpp"
 
@@ -206,7 +207,7 @@ namespace hmac_hash {
         char buf[2 * hmac_hash::SHA256::DIGEST_SIZE + 1];
         std::fill(buf, buf + (2 * hmac_hash::SHA256::DIGEST_SIZE + 1), '\0');
         for(size_t i = 0; i < hmac_hash::SHA256::DIGEST_SIZE; ++i) {
-            sprintf(buf + i * 2, "%02x", digest[i]);
+            std::snprintf(buf + i * 2, sizeof(buf) - i * 2, "%02x", digest[i]);
         }
         return std::string(buf, (2 * hmac_hash::SHA256::DIGEST_SIZE));
     }
diff --git a/sha512.cpp b/sha512.cpp
index 5aaa687..ba00b78 100644
--- a/sha512.cpp
+++ b/sha512.cpp
@@ -41,6 +41,7 @@
 
 #include <algorithm>
 #include <cstring>
+#include <cstdio>
 #include "sha512.hpp"
 
 #define SHA2_SHFR(x, n)    (x >> n)
@@ -241,7 +242,7 @@ namespace hmac_hash {
         char buf[2 * hmac_hash::SHA512::DIGEST_SIZE + 1];
         std::fill(buf, buf + (2 * hmac_hash::SHA512::DIGEST_SIZE + 1), '\0');
         for(size_t i = 0; i < hmac_hash::SHA512::DIGEST_SIZE; ++i){
-            sprintf(buf + i * 2, "%02x", digest[i]);
+            std::snprintf(buf + i * 2, sizeof(buf) - i * 2, "%02x", digest[i]);
         }
         return std::string(buf, (2 * hmac_hash::SHA512::DIGEST_SIZE));
     }