diff --git a/src/agent.c b/src/agent.c
index b7bd7594..c0d408fa 100644
--- a/src/agent.c
+++ b/src/agent.c
@@ -297,7 +297,8 @@ agent_transact_pageant(LIBSSH2_AGENT *agent, agent_transaction_ctx_t transctx)
         return _libssh2_error(agent->session, LIBSSH2_ERROR_AGENT_PROTOCOL,
                               "found no pageant");
 
-    sprintf(mapname, "PageantRequest%08x", (unsigned)GetCurrentThreadId());
+    snprintf(mapname, sizeof(mapname),
+             "PageantRequest%08x%c", (unsigned)GetCurrentThreadId(), '\0');
     filemap = CreateFileMapping(INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE,
                                 0, PAGEANT_MAX_MSGLEN, mapname);
 
diff --git a/src/channel.c b/src/channel.c
index d9208e43..f16412ce 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -1162,7 +1162,7 @@ channel_x11_req(LIBSSH2_CHANNEL *channel, int single_connection,
 
             _libssh2_random(buffer, LIBSSH2_X11_RANDOM_COOKIE_LEN / 2);
             for(i = 0; i < (LIBSSH2_X11_RANDOM_COOKIE_LEN / 2); i++) {
-                sprintf((char *)&s[i*2], "%02X", buffer[i]);
+                snprintf((char *)&s[i*2], 3, "%02X%c", buffer[i], '\0');
             }
         }
         s += cookie_len;