--- a/Win32OperatingSystem.st	Fri Dec 07 09:40:11 2018 +0100
+++ b/Win32OperatingSystem.st	Fri Dec 07 13:41:02 2018 +0100
@@ -16006,9 +16006,9 @@
 	or nil, to access the key (32/64) for the current application.
     "
 
-    |subKeyStringZ errorNumber|
-
-    subKeyStringZ := subKeyString asUnicode16StringZ.
+    |subKeyStringUtf16Z errorNumber|
+
+    subKeyStringUtf16Z := subKeyString asUnicode16StringZ.
 
 %{
     /* 
@@ -16021,7 +16021,7 @@
      * we're running on such old Windows - we call old RegDeleteKeyW(). 
      */
     static int initialized = 0;
-    static LONG (WINAPI *RegDeleteKeyExWPtr)(HKEY hKey, LPCTSTR lpSubKey, REGSAM  samDesired, DWORD   Reserved) = NULL;
+    static LONG (WINAPI *RegDeleteKeyExWPtr)(HKEY hKey, LPCTSTR lpSubKey, REGSAM samDesired, DWORD Reserved) = NULL;
     if (!initialized) {
         initialized = 1;
         HMODULE advapi32 = LoadLibrary("advapi32.dll");
@@ -16032,7 +16032,8 @@
             errorNumber = __MKSMALLINT(GetLastError());
             goto out;
         }
-        RegDeleteKeyExWPtr = GetProcAddress(advapi32, "RegDeleteKeyExW");        
+        RegDeleteKeyExWPtr = (LONG (*) (HKEY hKey, LPCTSTR lpSubKey, REGSAM samDesired, DWORD Reserved)) GetProcAddress(
+            advapi32, "RegDeleteKeyExW");        
     }    
     
     HKEY myKey, subKey = 0;
@@ -16051,11 +16052,11 @@
     }
 
     if (__isExternalAddressLike(__INST(handle))
-     && __isUnicode16String(subKeyStringZ)) {
+     && __isUnicode16String(subKeyStringUtf16Z)) {
 	myKey = (HKEY)__externalAddressVal(__INST(handle));
 	if (RegDeleteKeyExWPtr) {
 	    _retVal = RegDeleteKeyExWPtr(myKey,
-		                      __unicode16StringVal(subKeyStringZ),
+		                      (LPCTSTR) __unicode16StringVal(subKeyStringUtf16Z),
 		                      _flags,
 		                      0); // reserved	
 	} else {
@@ -16068,11 +16069,10 @@
 	     * for 32bit or 64bit view on Windows that does not support 
 	     * RegDeleteKeyExW().
 	     */
-	    if (flags != nil) {
-	        errorNumber = __MKSMALLINT(-1); // really stupid, should do better
-	        goto out;
-	    }
-	    _retVal = RegDeleteKeyW(myKey, __unicode16StringVal(subKeyStringZ));    
+	    if (flags != nil)  //if flag specified then return ERROR_INVALID_PARAMETER
+            _retVal = ERROR_INVALID_PARAMETER;
+	    else
+	        _retVal = RegDeleteKeyW(myKey, __unicode16StringVal(subKeyStringUtf16Z));    
 	}
 	if (_retVal == ERROR_SUCCESS) {
 	    RETURN (true);
@@ -16086,11 +16086,11 @@
 %}.
 
     errorNumber notNil ifTrue:[
-        errorNumber == -1 ifTrue:[
+        errorNumber == 87 ifTrue:[ "/ 87 (0x57) ... ERROR_INVALID_PARAMETER 
             self primitiveFailed: '32/64bit registry view requested but no RegDeleteKeyExW(). Windows too old?'
-        ] ifFalse:[
+        ].
 	    (OperatingSystem errorHolderForNumber:errorNumber) reportError.
-        ]
+        
     ].
     ^ false