diff --git a/dlls/ntdll/actctx.c b/dlls/ntdll/actctx.c
index e0c280af5bc..f64cb31a1f0 100644
--- a/dlls/ntdll/actctx.c
+++ b/dlls/ntdll/actctx.c
@@ -1098,7 +1098,7 @@ static WCHAR *build_assembly_dir(struct assembly_identity* ai)
     wcscat( ret, undW );
     wcscat( ret, key );
     wcscat( ret, undW );
-    NTDLL_swprintf( ret + wcslen(ret), version_formatW,
+    swprintf( ret + wcslen(ret), size - wcslen(ret), version_formatW,
               ai->version.major, ai->version.minor, ai->version.build, ai->version.revision );
     wcscat( ret, undW );
     wcscat( ret, lang );
@@ -1135,7 +1135,7 @@ static WCHAR *build_assembly_id( const struct assembly_identity *ai )
     WCHAR version[64], *ret;
     SIZE_T size = 0;
 
-    NTDLL_swprintf( version, version_formatW,
+    swprintf( version, ARRAY_SIZE(version), version_formatW,
               ai->version.major, ai->version.minor, ai->version.build, ai->version.revision );
     if (ai->name) size += wcslen(ai->name) * sizeof(WCHAR);
     if (ai->arch) size += wcslen(archW) + wcslen(ai->arch) + 2;
@@ -1981,7 +1981,7 @@ static int get_assembly_version(struct assembly *assembly, WCHAR *ret)
     WCHAR buff[25];
 
     if (!ret) ret = buff;
-    return NTDLL_swprintf(ret, fmtW, ver->major, ver->minor, ver->build, ver->revision);
+    return swprintf(ret, ARRAY_SIZE(buff), fmtW, ver->major, ver->minor, ver->build, ver->revision);
 }
 
 static void parse_window_class_elem( xmlbuf_t *xmlbuf, struct dll_redirect *dll,
@@ -3091,7 +3091,7 @@ static NTSTATUS get_manifest_in_associated_manifest( struct actctx_loader* acl,
 
         if (!(status = get_module_filename( module, &name, sizeof(dotManifestW) + 10*sizeof(WCHAR) )))
         {
-            if (resid != 1) NTDLL_swprintf( name.Buffer + wcslen(name.Buffer), fmtW, resid );
+            if (resid != 1) swprintf( name.Buffer + wcslen(name.Buffer), 10, fmtW, resid );
             wcscat( name.Buffer, dotManifestW );
             if (!RtlDosPathNameToNtPathName_U( name.Buffer, &nameW, NULL, NULL ))
                 status = STATUS_RESOURCE_DATA_NOT_FOUND;
@@ -3105,7 +3105,7 @@ static NTSTATUS get_manifest_in_associated_manifest( struct actctx_loader* acl,
                                         (wcslen(filename) + 10) * sizeof(WCHAR) + sizeof(dotManifestW) )))
             return STATUS_NO_MEMORY;
         wcscpy( buffer, filename );
-        if (resid != 1) NTDLL_swprintf( buffer + wcslen(buffer), fmtW, resid );
+        if (resid != 1) swprintf( buffer + wcslen(buffer), 10, fmtW, resid );
         wcscat( buffer, dotManifestW );
         RtlInitUnicodeString( &nameW, buffer );
     }
@@ -3131,17 +3131,14 @@ static WCHAR *lookup_manifest_file( HANDLE dir, struct assembly_identity *ai )
     UNICODE_STRING lookup_us;
     IO_STATUS_BLOCK io;
     const WCHAR *lang = ai->language;
-    unsigned int data_pos = 0, data_len;
+    unsigned int data_pos = 0, data_len, len;
     char buffer[8192];
 
     if (!lang || !wcsicmp( lang, neutralW )) lang = wildcardW;
 
-    if (!(lookup = RtlAllocateHeap( GetProcessHeap(), 0,
-                                    (wcslen(ai->arch) + wcslen(ai->name)
-                                     + wcslen(ai->public_key) + wcslen(lang) + 20) * sizeof(WCHAR)
-                                    + sizeof(lookup_fmtW) )))
-        return NULL;
-    NTDLL_swprintf( lookup, lookup_fmtW, ai->arch, ai->name, ai->public_key,
+    len = wcslen(ai->arch) + wcslen(ai->name) + wcslen(ai->public_key) + wcslen(lang) + 20 + ARRAY_SIZE(lookup_fmtW);
+    if (!(lookup = RtlAllocateHeap( GetProcessHeap(), 0, len * sizeof(WCHAR) ))) return NULL;
+    swprintf( lookup, len, lookup_fmtW, ai->arch, ai->name, ai->public_key,
               ai->version.major, ai->version.minor, lang );
     RtlInitUnicodeString( &lookup_us, lookup );
 
diff --git a/dlls/ntdll/atom.c b/dlls/ntdll/atom.c
index de0565094c8..1daaa1627c3 100644
--- a/dlls/ntdll/atom.c
+++ b/dlls/ntdll/atom.c
@@ -106,7 +106,7 @@ static ULONG integral_atom_name(WCHAR* buffer, ULONG len, RTL_ATOM atom)
     WCHAR tmp[16];
     int ret;
 
-    ret = NTDLL_swprintf( tmp, fmt, atom );
+    ret = swprintf( tmp, ARRAY_SIZE(tmp), fmt, atom );
     if (!len) return ret * sizeof(WCHAR);
     if (len <= ret) ret = len - 1;
     memcpy( buffer, tmp, ret * sizeof(WCHAR) );
diff --git a/dlls/ntdll/locale.c b/dlls/ntdll/locale.c
index 651da46aa6e..26295f260e8 100644
--- a/dlls/ntdll/locale.c
+++ b/dlls/ntdll/locale.c
@@ -583,16 +583,16 @@ static NTSTATUS open_nls_data_file( ULONG type, ULONG id, HANDLE *file )
         break;
     case NLS_SECTION_CASEMAP:
         if (id) return STATUS_UNSUCCESSFUL;
-        NTDLL_swprintf( buffer, keyfmtW, langW );
-        NTDLL_swprintf( value, langfmtW, LANGIDFROMLCID(system_lcid) );
+        swprintf( buffer, ARRAY_SIZE(buffer), keyfmtW, langW );
+        swprintf( value, ARRAY_SIZE(value), langfmtW, LANGIDFROMLCID(system_lcid) );
         break;
     case NLS_SECTION_CODEPAGE:
-        NTDLL_swprintf( buffer, keyfmtW, cpW );
-        NTDLL_swprintf( value, cpfmtW, id );
+        swprintf( buffer, ARRAY_SIZE(buffer), keyfmtW, cpW );
+        swprintf( value, ARRAY_SIZE(value), cpfmtW, id );
         break;
     case NLS_SECTION_NORMALIZE:
-        NTDLL_swprintf( buffer, keyfmtW, normW );
-        NTDLL_swprintf( value, normfmtW, id );
+        swprintf( buffer, ARRAY_SIZE(buffer), keyfmtW, normW );
+        swprintf( value, ARRAY_SIZE(value), normfmtW, id );
         break;
     default:
         return STATUS_INVALID_PARAMETER_1;
@@ -628,7 +628,7 @@ static NTSTATUS open_nls_data_file( ULONG type, ULONG id, HANDLE *file )
             name = intlW;
             break;
         case NLS_SECTION_CODEPAGE:
-            NTDLL_swprintf( buffer, cpdefaultW, id );
+            swprintf( buffer, ARRAY_SIZE(buffer), cpdefaultW, id );
             name = buffer;
             break;
         case NLS_SECTION_NORMALIZE:
@@ -650,7 +650,8 @@ static NTSTATUS open_nls_data_file( ULONG type, ULONG id, HANDLE *file )
     valueW.MaximumLength = (wcslen(name) + wcslen(dir) + 5) * sizeof(WCHAR);
     if (!(valueW.Buffer = RtlAllocateHeap( GetProcessHeap(), 0, valueW.MaximumLength )))
         return STATUS_NO_MEMORY;
-    valueW.Length = NTDLL_swprintf( valueW.Buffer, pathfmtW, dir, name ) * sizeof(WCHAR);
+    valueW.Length = swprintf( valueW.Buffer, valueW.MaximumLength/sizeof(WCHAR),
+                              pathfmtW, dir, name ) * sizeof(WCHAR);
     InitializeObjectAttributes( &attr, &valueW, 0, 0, NULL );
     status = NtOpenFile( file, GENERIC_READ, &attr, &io, FILE_SHARE_READ, FILE_SYNCHRONOUS_IO_ALERT );
     if (!status) TRACE( "found %s\n", debugstr_w( valueW.Buffer ));
diff --git a/dlls/ntdll/ntdll.spec b/dlls/ntdll/ntdll.spec
index c662db0c0f5..f3c06854014 100644
--- a/dlls/ntdll/ntdll.spec
+++ b/dlls/ntdll/ntdll.spec
@@ -1455,7 +1455,7 @@
 @ cdecl _memicmp(str str long)
 @ varargs _snprintf(ptr long str) NTDLL__snprintf
 @ varargs _snprintf_s(ptr long long str)
-@ varargs _snwprintf(ptr long wstr) NTDLL__snwprintf
+@ varargs _snwprintf(ptr long wstr)
 @ varargs _snwprintf_s(ptr long long wstr)
 @ varargs _swprintf(ptr wstr) NTDLL_swprintf
 @ cdecl _splitpath(str ptr ptr ptr ptr)
@@ -1472,9 +1472,9 @@
 @ cdecl _ultow(long ptr long)
 @ cdecl -norelay _vsnprintf(ptr long str ptr)
 @ cdecl _vsnprintf_s(ptr long str ptr)
-@ cdecl _vsnwprintf(ptr long wstr ptr) NTDLL__vsnwprintf
+@ cdecl _vsnwprintf(ptr long wstr ptr)
 @ cdecl _vsnwprintf_s(ptr long long wstr ptr)
-@ cdecl _vswprintf(ptr wstr ptr) NTDLL__vswprintf
+@ cdecl _vswprintf(ptr wstr ptr)
 @ cdecl _wcsicmp(wstr wstr) NTDLL__wcsicmp
 @ cdecl _wcslwr(wstr) NTDLL__wcslwr
 @ cdecl _wcsnicmp(wstr wstr long) NTDLL__wcsnicmp
@@ -1548,7 +1548,7 @@
 @ cdecl towupper(long) NTDLL_towupper
 @ stdcall vDbgPrintEx(long long str ptr)
 @ stdcall vDbgPrintExWithPrefix(str long long str ptr)
-@ cdecl vsprintf(ptr str ptr) NTDLL_vsprintf
+@ cdecl vsprintf(ptr str ptr)
 @ cdecl vsprintf_s(ptr long str ptr)
 @ cdecl vswprintf_s(ptr long wstr ptr)
 @ cdecl wcscat(wstr wstr) NTDLL_wcscat
diff --git a/dlls/ntdll/ntdll_misc.h b/dlls/ntdll/ntdll_misc.h
index 7c64515bd00..170aac85491 100644
--- a/dlls/ntdll/ntdll_misc.h
+++ b/dlls/ntdll/ntdll_misc.h
@@ -181,7 +181,6 @@ LPWSTR __cdecl NTDLL_wcsstr( LPCWSTR str, LPCWSTR sub );
 LPWSTR __cdecl NTDLL_wcstok( LPWSTR str, LPCWSTR delim );
 LONG   __cdecl NTDLL_wcstol( LPCWSTR s, LPWSTR *end, INT base );
 ULONG  __cdecl NTDLL_wcstoul( LPCWSTR s, LPWSTR *end, INT base );
-int    WINAPIV NTDLL_swprintf( WCHAR *str, const WCHAR *format, ... );
 
 #define memchr(p,c,n) NTDLL_memchr(p,c,n)
 #define strcat(d,s) NTDLL_strcat(d,s)
diff --git a/dlls/ntdll/printf.c b/dlls/ntdll/printf.c
index f753aef5552..16f64002d41 100644
--- a/dlls/ntdll/printf.c
+++ b/dlls/ntdll/printf.c
@@ -618,7 +618,7 @@ int CDECL _vsnprintf( char *str, size_t len, const char *format, __ms_va_list ar
 /***********************************************************************
  *                  _vsnwprintf   (NTDLL.@)
  */
-int CDECL NTDLL__vsnwprintf( WCHAR *str, SIZE_T len, const WCHAR *format, __ms_va_list args )
+int CDECL _vsnwprintf( WCHAR *str, size_t len, const WCHAR *format, __ms_va_list args )
 {
     pf_output out;
     int r;
@@ -637,7 +637,7 @@ int CDECL NTDLL__vsnwprintf( WCHAR *str, SIZE_T len, const WCHAR *format, __ms_v
 /*********************************************************************
  *                  _snprintf   (NTDLL.@)
  */
-int WINAPIV NTDLL__snprintf( char *str, SIZE_T len, const char *format, ... )
+int WINAPIV NTDLL__snprintf( char *str, size_t len, const char *format, ... )
 {
     int ret;
     __ms_va_list valist;
@@ -652,13 +652,13 @@ int WINAPIV NTDLL__snprintf( char *str, SIZE_T len, const char *format, ... )
 /***********************************************************************
  *                  _snwprintf   (NTDLL.@)
  */
-int WINAPIV NTDLL__snwprintf( WCHAR *str, SIZE_T len, const WCHAR *format, ... )
+int WINAPIV _snwprintf( WCHAR *str, size_t len, const WCHAR *format, ... )
 {
     int ret;
     __ms_va_list valist;
 
     __ms_va_start(valist, format);
-    ret = NTDLL__vsnwprintf( str, len, format, valist );
+    ret = _vsnwprintf( str, len, format, valist );
     __ms_va_end(valist);
     return ret;
 }
@@ -748,7 +748,7 @@ int WINAPIV _snwprintf_s( WCHAR *str, size_t size, size_t len, const WCHAR *form
 /*********************************************************************
  *                  vsprintf   (NTDLL.@)
  */
-int CDECL NTDLL_vsprintf( char *str, const char *format, __ms_va_list args )
+int CDECL vsprintf( char *str, const char *format, __ms_va_list args )
 {
     return _vsnprintf( str, size_max, format, args );
 }
@@ -766,9 +766,9 @@ int CDECL vsprintf_s( char *str, size_t size, const char *format, __ms_va_list a
 /*********************************************************************
  *                  _vswprintf   (NTDLL.@)
  */
-int CDECL NTDLL__vswprintf( WCHAR *str, const WCHAR *format, __ms_va_list args )
+int CDECL _vswprintf( WCHAR *str, const WCHAR *format, __ms_va_list args )
 {
-    return NTDLL__vsnwprintf( str, size_max, format, args );
+    return _vsnwprintf( str, size_max, format, args );
 }
 
 
@@ -820,7 +820,7 @@ int WINAPIV NTDLL_swprintf( WCHAR *str, const WCHAR *format, ... )
     __ms_va_list valist;
 
     __ms_va_start(valist, format);
-    ret = NTDLL__vsnwprintf( str, size_max, format, valist );
+    ret = _vsnwprintf( str, size_max, format, valist );
     __ms_va_end(valist);
     return ret;
 }
diff --git a/dlls/ntdll/process.c b/dlls/ntdll/process.c
index e5b56381964..992721d133f 100644
--- a/dlls/ntdll/process.c
+++ b/dlls/ntdll/process.c
@@ -204,6 +204,7 @@ NTSTATUS restart_process( RTL_USER_PROCESS_PARAMETERS *params, NTSTATUS status )
     static const WCHAR comW[] = {'.','c','o','m',0};
     static const WCHAR pifW[] = {'.','p','i','f',0};
 
+    DWORD len;
     WCHAR *p, *cmdline;
     UNICODE_STRING pathW, cmdW;
 
@@ -226,12 +227,11 @@ NTSTATUS restart_process( RTL_USER_PROCESS_PARAMETERS *params, NTSTATUS status )
     case STATUS_INVALID_IMAGE_WIN_16:
     case STATUS_INVALID_IMAGE_NE_FORMAT:
     case STATUS_INVALID_IMAGE_PROTECT:
-        cmdline = RtlAllocateHeap( GetProcessHeap(), 0,
-                                   (wcslen(system_dir) + wcslen(winevdm) + 16 +
-                                    wcslen(params->ImagePathName.Buffer) +
-                                    wcslen(params->CommandLine.Buffer)) * sizeof(WCHAR));
-        if (!cmdline) return STATUS_NO_MEMORY;
-        NTDLL_swprintf( cmdline, argsW, (is_win64 || is_wow64) ? syswow64_dir : system_dir,
+        len = (wcslen(system_dir) + wcslen(winevdm) + 16 + wcslen(params->ImagePathName.Buffer) +
+               wcslen(params->CommandLine.Buffer));
+        if (!(cmdline = RtlAllocateHeap( GetProcessHeap(), 0, len * sizeof(WCHAR) )))
+            return STATUS_NO_MEMORY;
+        swprintf( cmdline, len, argsW, (is_win64 || is_wow64) ? syswow64_dir : system_dir,
                   winevdm, params->ImagePathName.Buffer, params->CommandLine.Buffer );
         RtlInitUnicodeString( &pathW, winevdm );
         RtlInitUnicodeString( &cmdW, cmdline );
diff --git a/dlls/ntdll/rtl.c b/dlls/ntdll/rtl.c
index 14a44c3e2f9..c32c63a880d 100644
--- a/dlls/ntdll/rtl.c
+++ b/dlls/ntdll/rtl.c
@@ -1319,11 +1319,11 @@ NTSTATUS WINAPI RtlIpv4AddressToStringExW(const IN_ADDR *pin, USHORT port, LPWST
 
     TRACE("(%p:0x%x, %d, %p, %p:%d)\n", pin, pin->S_un.S_addr, port, buffer, psize, *psize);
 
-    needed = NTDLL_swprintf(tmp_ip, fmt_ip,
+    needed = swprintf(tmp_ip, ARRAY_SIZE(tmp_ip), fmt_ip,
                       pin->S_un.S_un_b.s_b1, pin->S_un.S_un_b.s_b2,
                       pin->S_un.S_un_b.s_b3, pin->S_un.S_un_b.s_b4);
 
-    if (port) needed += NTDLL_swprintf(tmp_ip + needed, fmt_port, ntohs(port));
+    if (port) needed += swprintf(tmp_ip + needed, ARRAY_SIZE(tmp_ip) - needed, fmt_port, ntohs(port));
 
     if (*psize > needed) {
         *psize = needed + 1;
diff --git a/dlls/ntdll/rtlstr.c b/dlls/ntdll/rtlstr.c
index 05cb34224c0..d8ff81b8050 100644
--- a/dlls/ntdll/rtlstr.c
+++ b/dlls/ntdll/rtlstr.c
@@ -1699,7 +1699,7 @@ NTSTATUS WINAPI RtlStringFromGUID(const GUID* guid, UNICODE_STRING *str)
     str->Length = str->MaximumLength = 0;
     return STATUS_NO_MEMORY;
   }
-  NTDLL_swprintf(str->Buffer, szFormat, guid->Data1, guid->Data2, guid->Data3,
+  swprintf(str->Buffer, str->MaximumLength/sizeof(WCHAR), szFormat, guid->Data1, guid->Data2, guid->Data3,
           guid->Data4[0], guid->Data4[1], guid->Data4[2], guid->Data4[3],
           guid->Data4[4], guid->Data4[5], guid->Data4[6], guid->Data4[7]);
 
diff --git a/dlls/ntdll/sec.c b/dlls/ntdll/sec.c
index 2447a405861..5876e06c5b5 100644
--- a/dlls/ntdll/sec.c
+++ b/dlls/ntdll/sec.c
@@ -1820,13 +1820,14 @@ NTSTATUS WINAPI RtlConvertSidToUnicodeString(
     DWORD i, len;
 
     *p++ = 'S';
-    p += NTDLL_swprintf( p, formatW, sid->Revision );
-    p += NTDLL_swprintf( p, formatW, MAKELONG( MAKEWORD( sid->IdentifierAuthority.Value[5],
-                                                   sid->IdentifierAuthority.Value[4] ),
-                                         MAKEWORD( sid->IdentifierAuthority.Value[3],
-                                                   sid->IdentifierAuthority.Value[2] )));
+    p += swprintf( p, ARRAY_SIZE(buffer) - (p - buffer), formatW, sid->Revision );
+    p += swprintf( p, ARRAY_SIZE(buffer) - (p - buffer), formatW,
+                   MAKELONG( MAKEWORD( sid->IdentifierAuthority.Value[5],
+                                       sid->IdentifierAuthority.Value[4] ),
+                             MAKEWORD( sid->IdentifierAuthority.Value[3],
+                                       sid->IdentifierAuthority.Value[2] )));
     for (i = 0; i < sid->SubAuthorityCount; i++)
-        p += NTDLL_swprintf( p, formatW, sid->SubAuthority[i] );
+        p += swprintf( p, ARRAY_SIZE(buffer) - (p - buffer), formatW, sid->SubAuthority[i] );
 
     len = (p + 1 - buffer) * sizeof(WCHAR);