diff --git a/src/klibc/rt_vsnprintf_std.c b/src/klibc/rt_vsnprintf_std.c
index 481c99013b00..24ff4c7ae3cf 100644
--- a/src/klibc/rt_vsnprintf_std.c
+++ b/src/klibc/rt_vsnprintf_std.c
@@ -371,7 +371,9 @@ static inline output_gadget_t buffer_gadget(char* buffer, size_t buffer_size)
 static inline printf_size_t strnlen_s_(const char* str, printf_size_t maxsize)
 {
   const char* s;
-  for (s = str; *s && maxsize--; ++s);
+  // check the bound before dereferencing,
+  // so that at most maxsize characters are read.
+  for (s = str; maxsize && *s; ++s, --maxsize);
   return (printf_size_t)(s - str);
 }
 
@@ -1053,7 +1055,14 @@ static inline void format_string_loop(output_gadget_t* output, const char* forma
       }
       else if (*format == '*') {
         const int precision_ = va_arg(args, int);
-        precision = precision_ > 0 ? (printf_size_t) precision_ : 0U;
+        if (precision_ < 0)
+        {
+            flags &= ~FLAGS_PRECISION;
+        }
+        else
+        {
+            precision = (printf_size_t)precision_;
+        }
         ADVANCE_IN_FORMAT_STRING(format);
       }
     }
diff --git a/src/klibc/rt_vsnprintf_tiny.c b/src/klibc/rt_vsnprintf_tiny.c
index 36811048a993..750c916991df 100644
--- a/src/klibc/rt_vsnprintf_tiny.c
+++ b/src/klibc/rt_vsnprintf_tiny.c
@@ -83,6 +83,7 @@ static char *print_number(char *buf,
     static const char large_digits[] = "0123456789ABCDEF";
     int i = 0;
     int size = 0;
+    int is_zero = 0;
 
     size = s;
 
@@ -151,6 +152,7 @@ static char *print_number(char *buf,
     }
 
     i = 0;
+    is_zero = (num == 0);
     if (num == 0)
     {
         tmp[i++] = '0';
@@ -253,7 +255,7 @@ static char *print_number(char *buf,
     }
 
     /* put number in the temporary buffer */
-    while (i-- > 0 && (precision_bak != 0))
+    while (i-- > 0 && !((precision_bak == 0) && is_zero))
     {
         if (buf < end)
         {
@@ -382,8 +384,12 @@ int rt_vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
                 ++fmt;
                 /* it's the next argument */
                 precision = va_arg(args, int);
+                if (precision < 0)
+                {
+                    precision = -1;
+                }
             }
-            if (precision < 0)
+            else
             {
                 precision = 0;
             }
@@ -451,12 +457,7 @@ int rt_vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
                 s = "(null)";
             }
 
-            for (len = 0; (len != field_width) && (s[len] != '\0'); len++);
-
-            if (precision > 0 && len > precision)
-            {
-                len = precision;
-            }
+            for (len = 0; (precision < 0 || len < precision) && (s[len] != '\0'); len++);
 
             if (!(flags & LEFT))
             {
diff --git a/src/klibc/utest/TC_rt_sprintf.c b/src/klibc/utest/TC_rt_sprintf.c
index d8bba42c08c8..1e9bf8449563 100644
--- a/src/klibc/utest/TC_rt_sprintf.c
+++ b/src/klibc/utest/TC_rt_sprintf.c
@@ -334,9 +334,7 @@ SPRINTF_TEST_CASE(specifier)
 SPRINTF_TEST_CASE(width)
 {
     char buffer[base_buffer_size];
-#ifdef RT_KLIBC_USING_VSNPRINTF_STANDARD
     SPRINTF_CHECK("Hello testing",           buffer, "%1s", "Hello testing");
-#endif /* RT_KLIBC_USING_VSNPRINTF_STANDARD */
     SPRINTF_CHECK("1024",                    buffer, "%1d", 1024);
     SPRINTF_CHECK("-1024",                   buffer, "%1d", -1024);
     SPRINTF_CHECK("1024",                    buffer, "%1i", 1024);
@@ -837,10 +835,6 @@ SPRINTF_TEST_CASE(tiny_floating_point_values)
 SPRINTF_TEST_CASE(length)
 {
     char buffer[base_buffer_size];
-    SPRINTF_CHECK("",                        buffer, "%.0s", "Hello testing");
-    SPRINTF_CHECK("                    ",    buffer, "%20.0s", "Hello testing");
-    SPRINTF_CHECK("",                        buffer, "%.s", "Hello testing");
-    SPRINTF_CHECK("                    ",    buffer, "%20.s", "Hello testing");
     SPRINTF_CHECK("                1024",    buffer, "%20.0d", 1024);
     SPRINTF_CHECK("               -1024",    buffer, "%20.0d", -1024);
     SPRINTF_CHECK("                    ",    buffer, "%20.d", 0);
@@ -972,6 +966,19 @@ SPRINTF_TEST_CASE(pointer)
 SPRINTF_TEST_CASE(string_length)
 {
     char buffer[base_buffer_size];
+#if !defined(RT_KLIBC_USING_LIBC_VSNPRINTF)
+    char unterminated[] = { 'A', 'B', 'C' };
+#endif
+
+    SPRINTF_CHECK("", buffer, "%.0s", "Hello testing");
+    SPRINTF_CHECK("                    ", buffer, "%20.0s", "Hello testing");
+    SPRINTF_CHECK("", buffer, "%.s", "Hello testing");
+    SPRINTF_CHECK("                    ", buffer, "%20.s", "Hello testing");
+    SPRINTF_CHECK("", buffer, "%.*s", 0, "Hello testing");
+#if !defined(RT_KLIBC_USING_LIBC_VSNPRINTF)
+    SPRINTF_CHECK("Hello testing", buffer, "%.*s", -1, "Hello testing");
+    SPRINTF_CHECK("ABC", buffer, "%.3s", unterminated);
+#endif
     SPRINTF_CHECK("This",                    buffer, "%.4s", "This is a test");
     SPRINTF_CHECK("test",                    buffer, "%.4s", "test");
     SPRINTF_CHECK("123",                     buffer, "%.7s", "123");
@@ -989,14 +996,16 @@ SPRINTF_TEST_CASE(misc)
 {
     char buffer[base_buffer_size];
     SPRINTF_CHECK("53000atest-20 bit",       buffer, "%u%u%ctest%d %s", 5, 3000, 'a', -20, "bit");
-#ifdef RT_KLIBC_USING_VSNPRINTF_DECIMAL_SPECIFIERS
-    SPRINTF_CHECK("0.33",                    buffer, "%.*f", 2, 0.33333333);
     SPRINTF_CHECK("1",                       buffer, "%.*d", -1, 1);
     SPRINTF_CHECK("foo",                     buffer, "%.3s", "foobar");
     SPRINTF_CHECK(" ",                       buffer, "% .0d", 0);
+    SPRINTF_CHECK("5", buffer, "%.0d", 5);
+    SPRINTF_CHECK("", buffer, "%.0d", 0);
     SPRINTF_CHECK("     00004",              buffer, "%10.5d", 4);
     SPRINTF_CHECK("hi x",                    buffer, "%*sx", -3, "hi");
     SPRINTF_CHECK("00123               ",    buffer, "%-20.5i", 123);
+#ifdef RT_KLIBC_USING_VSNPRINTF_DECIMAL_SPECIFIERS
+    SPRINTF_CHECK("0.33", buffer, "%.*f", 2, 0.33333333);
     SPRINTF_CHECK("-67224.546875000000000000", buffer, "%.18f", -67224.546875);
 #endif /* RT_KLIBC_USING_VSNPRINTF_DECIMAL_SPECIFIERS */
 #ifdef RT_KLIBC_USING_VSNPRINTF_EXPONENTIAL_SPECIFIERS