diff --git a/dlls/ntdll/actctx.c b/dlls/ntdll/actctx.c
index cd17c6c1352..d53ddf86949 100644
--- a/dlls/ntdll/actctx.c
+++ b/dlls/ntdll/actctx.c
@@ -3141,10 +3141,10 @@ static WCHAR *lookup_manifest_file( HANDLE dir, struct assembly_identity *ai )
             else data_pos = data_len;
 
             tmp = dir_info->FileName + (strchrW(lookup, '*') - lookup);
-            build = atoiW(tmp);
+            build = wcstoul( tmp, NULL, 10 );
             if (build < min_build) continue;
             tmp = strchrW(tmp, '.') + 1;
-            revision = atoiW(tmp);
+            revision = wcstoul( tmp, NULL, 10 );
             if (build == min_build && revision < min_revision) continue;
             tmp = strchrW(tmp, '_') + 1;
             tmp = strchrW(tmp, '_') + 1;
diff --git a/dlls/ntdll/ntdll_misc.h b/dlls/ntdll/ntdll_misc.h
index fe0d1755d0b..ccb2e76c200 100644
--- a/dlls/ntdll/ntdll_misc.h
+++ b/dlls/ntdll/ntdll_misc.h
@@ -301,6 +301,7 @@ ULONG  __cdecl NTDLL_wcstoul( LPCWSTR s, LPWSTR *end, INT base );
 #define towupper(c) NTDLL_towupper(c)
 #define wcslwr(s) NTDLL__wcslwr(s)
 #define wcsupr(s) NTDLL__wcsupr(s)
+#define wcstoul(s,e,b) NTDLL_wcstoul(s,e,b)
 
 /* convert from straight ASCII to Unicode without depending on the current codepage */
 static inline void ascii_to_unicode( WCHAR *dst, const char *src, size_t len )
diff --git a/dlls/ntdll/version.c b/dlls/ntdll/version.c
index 4994dbbb5e5..e5fb63e7782 100644
--- a/dlls/ntdll/version.c
+++ b/dlls/ntdll/version.c
@@ -285,9 +285,9 @@ static BOOL get_nt_registry_version( RTL_OSVERSIONINFOEXW *version )
         if (p)
         {
             *p++ = 0;
-            version->dwMinorVersion = atoiW( p );
+            version->dwMinorVersion = wcstoul( p, NULL, 10 );
         }
-        version->dwMajorVersion = atoiW( str );
+        version->dwMajorVersion = wcstoul( str, NULL, 10 );
     }
 
     if (version->dwMajorVersion)   /* we got the main version, now fetch the other fields */
@@ -302,7 +302,7 @@ static BOOL get_nt_registry_version( RTL_OSVERSIONINFOEXW *version )
         {
             WCHAR *str = (WCHAR *)info->Data;
             str[info->DataLength / sizeof(WCHAR)] = 0;
-            version->dwBuildNumber = atoiW( str );
+            version->dwBuildNumber = wcstoul( str, NULL, 10 );
         }
 
         /* get version description */
@@ -400,7 +400,7 @@ static BOOL get_win9x_registry_version( RTL_OSVERSIONINFOEXW *version )
         str[info->DataLength / sizeof(WCHAR)] = 0;
         p = strchrW( str, '.' );
         if (p) *p++ = 0;
-        version->dwMajorVersion = atoiW( str );
+        version->dwMajorVersion = wcstoul( str, NULL, 10 );
         if (p)
         {
             str = p;
@@ -408,9 +408,9 @@ static BOOL get_win9x_registry_version( RTL_OSVERSIONINFOEXW *version )
             if (p)
             {
                 *p++ = 0;
-                version->dwBuildNumber = atoiW( p );
+                version->dwBuildNumber = wcstoul( p, NULL, 10 );
             }
-            version->dwMinorVersion = atoiW( str );
+            version->dwMinorVersion = wcstoul( str, NULL, 10 );
         }
         /* build number contains version too on Win9x */
         version->dwBuildNumber |= MAKEWORD( version->dwMinorVersion, version->dwMajorVersion ) << 16;