diff --git a/dlls/msvcr100/msvcr100.spec b/dlls/msvcr100/msvcr100.spec
index 4323e457a50..646137daa0e 100644
--- a/dlls/msvcr100/msvcr100.spec
+++ b/dlls/msvcr100/msvcr100.spec
@@ -1609,7 +1609,7 @@
 @ cdecl _wtof_l(wstr ptr) msvcrt._wtof_l
 @ cdecl _wtoi(wstr) msvcrt._wtoi
 @ cdecl -ret64 _wtoi64(wstr) msvcrt._wtoi64
-@ stub _wtoi64_l
+@ cdecl -ret64 _wtoi64_l(wstr ptr) msvcrt._wtoi64_l
 @ cdecl _wtoi_l(wstr ptr) msvcrt._wtoi_l
 @ cdecl _wtol(wstr) msvcrt._wtol
 @ cdecl _wtol_l(wstr ptr) msvcrt._wtol_l
diff --git a/dlls/msvcr110/msvcr110.spec b/dlls/msvcr110/msvcr110.spec
index 57bd10747ac..b82a58e02ed 100644
--- a/dlls/msvcr110/msvcr110.spec
+++ b/dlls/msvcr110/msvcr110.spec
@@ -1967,7 +1967,7 @@
 @ cdecl _wtof_l(wstr ptr) msvcrt._wtof_l
 @ cdecl _wtoi(wstr) msvcrt._wtoi
 @ cdecl -ret64 _wtoi64(wstr) msvcrt._wtoi64
-@ stub _wtoi64_l
+@ cdecl -ret64 _wtoi64_l(wstr ptr) msvcrt._wtoi64_l
 @ cdecl _wtoi_l(wstr ptr) msvcrt._wtoi_l
 @ cdecl _wtol(wstr) msvcrt._wtol
 @ cdecl _wtol_l(wstr ptr) msvcrt._wtol_l
diff --git a/dlls/msvcr80/msvcr80.spec b/dlls/msvcr80/msvcr80.spec
index b70d4fb9c5a..0a0adf654a5 100644
--- a/dlls/msvcr80/msvcr80.spec
+++ b/dlls/msvcr80/msvcr80.spec
@@ -1291,7 +1291,7 @@
 @ cdecl _wtof_l(wstr ptr) msvcrt._wtof_l
 @ cdecl _wtoi(wstr) msvcrt._wtoi
 @ cdecl -ret64 _wtoi64(wstr) msvcrt._wtoi64
-@ stub _wtoi64_l
+@ cdecl -ret64 _wtoi64_l(wstr ptr) msvcrt._wtoi64_l
 @ cdecl _wtoi_l(wstr ptr) msvcrt._wtoi_l
 @ cdecl _wtol(wstr) msvcrt._wtol
 @ cdecl _wtol_l(wstr ptr) msvcrt._wtol_l
diff --git a/dlls/msvcr90/msvcr90.spec b/dlls/msvcr90/msvcr90.spec
index 36cf2e4a8b6..382a52e717c 100644
--- a/dlls/msvcr90/msvcr90.spec
+++ b/dlls/msvcr90/msvcr90.spec
@@ -1264,7 +1264,7 @@
 @ cdecl _wtof_l(wstr ptr) msvcrt._wtof_l
 @ cdecl _wtoi(wstr) msvcrt._wtoi
 @ cdecl -ret64 _wtoi64(wstr) msvcrt._wtoi64
-@ stub _wtoi64_l
+@ cdecl -ret64 _wtoi64_l(wstr ptr) msvcrt._wtoi64_l
 @ cdecl _wtoi_l(wstr ptr) msvcrt._wtoi_l
 @ cdecl _wtol(wstr) msvcrt._wtol
 @ cdecl _wtol_l(wstr ptr) msvcrt._wtol_l
diff --git a/dlls/msvcrt/msvcrt.spec b/dlls/msvcrt/msvcrt.spec
index 7cfc3704461..acf53aa58c2 100644
--- a/dlls/msvcrt/msvcrt.spec
+++ b/dlls/msvcrt/msvcrt.spec
@@ -1229,8 +1229,8 @@
 @ cdecl _wtof(wstr) MSVCRT__wtof
 @ cdecl _wtof_l(wstr ptr) MSVCRT__wtof_l
 @ cdecl _wtoi(wstr) MSVCRT__wtoi
-@ cdecl -ret64 _wtoi64(wstr) ntdll._wtoi64
-# stub -ret64 _wtoi64_l(wstr ptr)
+@ cdecl -ret64 _wtoi64(wstr)
+@ cdecl -ret64 _wtoi64_l(wstr ptr)
 @ cdecl _wtoi_l(wstr ptr) MSVCRT__wtoi_l
 @ cdecl _wtol(wstr) MSVCRT__wtol
 @ cdecl _wtol_l(wstr ptr) MSVCRT__wtol_l
diff --git a/dlls/msvcrt/wcs.c b/dlls/msvcrt/wcs.c
index 1cf227651ce..4b23671320f 100644
--- a/dlls/msvcrt/wcs.c
+++ b/dlls/msvcrt/wcs.c
@@ -1888,3 +1888,38 @@ MSVCRT_wchar_t* CDECL MSVCRT_wcsstr(const MSVCRT_wchar_t *str, const MSVCRT_wcha
 {
     return strstrW(str, sub);
 }
+
+/*********************************************************************
+ *              _wtoi64_l (MSVCRT.@)
+ */
+__int64 CDECL _wtoi64_l(const MSVCRT_wchar_t *str, MSVCRT__locale_t locale)
+{
+    ULONGLONG RunningTotal = 0;
+    char bMinus = 0;
+
+    while (isspaceW(*str)) {
+        str++;
+    } /* while */
+
+    if (*str == '+') {
+        str++;
+    } else if (*str == '-') {
+        bMinus = 1;
+        str++;
+    } /* if */
+
+    while (*str >= '0' && *str <= '9') {
+        RunningTotal = RunningTotal * 10 + *str - '0';
+        str++;
+    } /* while */
+
+    return bMinus ? -RunningTotal : RunningTotal;
+}
+
+/*********************************************************************
+ *              _wtoi64 (MSVCRT.@)
+ */
+__int64 CDECL _wtoi64(const MSVCRT_wchar_t *str)
+{
+    return _wtoi64_l(str, NULL);
+}