diff --git a/kernel/src/std/stdio.cpp b/kernel/src/std/stdio.cpp
index 08819639..18af8db5 100644
--- a/kernel/src/std/stdio.cpp
+++ b/kernel/src/std/stdio.cpp
@@ -228,6 +228,7 @@ int sprintf(char* __s, const char* fmt, ...)
 {
     va_list ap;
     va_start(ap, fmt);
+    if (__s) *__s = 0;
     int written = internal_printf(
         fmt,
         [&](const char* s) {
@@ -242,6 +243,7 @@ int snprintf(char* __s, size_t max, const char* fmt, ...)
 {
     va_list ap;
     va_start(ap, fmt);
+    if (__s && max) *__s = 0;
     int written = internal_printf(
         fmt,
         [&](const char* s) {
@@ -266,6 +268,7 @@ int vkprintf(const char* fmt, va_list ap)
 
 int vsprintf(char* __s, const char* fmt, va_list ap)
 {
+    *__s = 0;
     return internal_printf(
         fmt,
         [&](const char* s) {
@@ -276,6 +279,7 @@ int vsprintf(char* __s, const char* fmt, va_list ap)
 
 int vsnprintf(char* __s, size_t max, const char* fmt, va_list ap)
 {
+    if (max) *__s = 0;
     return internal_printf(
         fmt,
         [&](const char* s) {
diff --git a/libs/libc/src/printf.cpp b/libs/libc/src/printf.cpp
index e4bb9847..e47568c1 100644
--- a/libs/libc/src/printf.cpp
+++ b/libs/libc/src/printf.cpp
@@ -261,6 +261,7 @@ extern "C"
 
     int vsprintf(char* str, const char* format, va_list ap)
     {
+        if (str) *str = 0; // so strncat starts from the beginning
         return internal_printf(
             format,
             [&](const char* s) {
@@ -271,6 +272,7 @@ extern "C"
 
     int vsnprintf(char* str, size_t max, const char* format, va_list ap)
     {
+        if (max && str) *str = 0; // so strncat starts from the beginning
         return internal_printf(
             format,
             [&](const char* s) {