diff --git a/lib/std/os/windows/ntdll.zig b/lib/std/os/windows/ntdll.zig
index ca033cc367..bf9dc9bd2f 100644
--- a/lib/std/os/windows/ntdll.zig
+++ b/lib/std/os/windows/ntdll.zig
@@ -229,12 +229,6 @@ pub extern "ntdll" fn RtlEqualUnicodeString(
     CaseInSensitive: BOOLEAN,
 ) callconv(WINAPI) BOOLEAN;
 
-pub extern "ntdll" fn RtlUpcaseUnicodeString(
-    DestinationString: *UNICODE_STRING,
-    SourceString: *const UNICODE_STRING,
-    AllocateDestinationString: BOOLEAN,
-) callconv(WINAPI) NTSTATUS;
-
 pub extern "ntdll" fn RtlUpcaseUnicodeChar(
     SourceCharacter: u16,
 ) callconv(WINAPI) u16;