diff --git a/dlls/api-ms-win-core-winrt-string-l1-1-0/api-ms-win-core-winrt-string-l1-1-0.spec b/dlls/api-ms-win-core-winrt-string-l1-1-0/api-ms-win-core-winrt-string-l1-1-0.spec
index f629bcfbcb8..dc67deb7867 100644
--- a/dlls/api-ms-win-core-winrt-string-l1-1-0/api-ms-win-core-winrt-string-l1-1-0.spec
+++ b/dlls/api-ms-win-core-winrt-string-l1-1-0/api-ms-win-core-winrt-string-l1-1-0.spec
@@ -22,6 +22,6 @@
 @ stub WindowsReplaceString
 @ stdcall WindowsStringHasEmbeddedNull(ptr ptr) combase.WindowsStringHasEmbeddedNull
 @ stdcall WindowsSubstring(ptr long ptr) combase.WindowsSubstring
-@ stub WindowsSubstringWithSpecifiedLength
+@ stdcall WindowsSubstringWithSpecifiedLength(ptr long long ptr) combase.WindowsSubstringWithSpecifiedLength
 @ stub WindowsTrimStringEnd
 @ stub WindowsTrimStringStart
diff --git a/dlls/combase/combase.spec b/dlls/combase/combase.spec
index e7c8866523f..fcd59474ee1 100644
--- a/dlls/combase/combase.spec
+++ b/dlls/combase/combase.spec
@@ -303,6 +303,6 @@
 @ stub WindowsReplaceString
 @ stdcall WindowsStringHasEmbeddedNull(ptr ptr)
 @ stdcall WindowsSubstring(ptr long ptr)
-@ stub WindowsSubstringWithSpecifiedLength
+@ stdcall WindowsSubstringWithSpecifiedLength(ptr long long ptr)
 @ stub WindowsTrimStringEnd
 @ stub WindowsTrimStringStart
diff --git a/dlls/combase/string.c b/dlls/combase/string.c
index 2146d6179bb..49d76958d94 100644
--- a/dlls/combase/string.c
+++ b/dlls/combase/string.c
@@ -307,6 +307,28 @@ HRESULT WINAPI WindowsSubstring(HSTRING str, UINT32 start, HSTRING *out)
     return WindowsCreateString(&priv->buffer[start], len - start, out);
 }
 
+/***********************************************************************
+ *      WindowsSubstringWithSpecifiedLength (combase.@)
+ */
+HRESULT WINAPI WindowsSubstringWithSpecifiedLength(HSTRING str, UINT32 start, UINT32 len, HSTRING *out)
+{
+    struct hstring_private *priv = impl_from_HSTRING(str);
+
+    TRACE("(%p, %u, %u, %p)\n", str, start, len, out);
+
+    if (out == NULL)
+        return E_INVALIDARG;
+    if (start + len < start ||
+        start + len > WindowsGetStringLen(str))
+        return E_BOUNDS;
+    if (len == 0)
+    {
+        *out = NULL;
+        return S_OK;
+    }
+    return WindowsCreateString(&priv->buffer[start], len, out);
+}
+
 /***********************************************************************
  *      WindowsIsStringEmpty (combase.@)
  */