diff -r 6054b4897eed -r d18a4fe6b86a Win32OperatingSystem.st
--- a/Win32OperatingSystem.st	Thu Aug 18 15:48:36 2016 +0200
+++ b/Win32OperatingSystem.st	Thu Aug 18 16:37:37 2016 +0200
@@ -7960,7 +7960,7 @@
     "Modified: / 03-08-2010 / 16:59:26 / cg"
 !
 
-primOpenMutex:lpSecurityDescriptor initialOwner:bInitialOwner name:lpName
+primOpenMutex:dwDesiredAccess initialOwner:bInitialOwner name:lpName
     "If the function succeeds, the return value is a handle to the mutex object.
      If the function fails, the return value is NULL. To get extended error information, call GetLastError.
      If a named mutex does not exist, the function fails and GetLastError returns ERROR_FILE_NOT_FOUND."
@@ -7971,23 +7971,22 @@
 %{
     if (__isString(lpName)
      && ((bInitialOwner == true) || (bInitialOwner == false))) {
-	void *c_descr = NULL;
-	char *c_name;
-	BOOL c_initialOwner = (bInitialOwner == true);
-	HANDLE c_handle;
-
-	c_name = __stringVal(lpName);
-
-	if (lpSecurityDescriptor != nil) {
-	    if (__isExternalAddressLike(lpSecurityDescriptor)
-	     || __isExternalBytesLike(lpSecurityDescriptor) ) {
-		c_descr = __externalAddressVal(lpSecurityDescriptor);
-	    } else
-		goto badArg;
-	}
-	c_handle = OpenMutexA(c_descr, c_initialOwner, c_name);
-	__externalAddressVal(handle) = c_handle;
-	RETURN(handle);
+        DWORD c_dwDesiredAccess = 0;
+        char *c_name;
+        BOOL c_initialOwner = (bInitialOwner == true);
+        HANDLE c_handle;
+
+        c_name = __stringVal(lpName);
+
+        if (dwDesiredAccess != nil) {
+            if (! isSmallInteger(dwDesiredAccess)) {       
+                goto badArg;
+            }
+            c_dwDesiredAccess = __intVal(dwDesiredAccess);
+        }
+        c_handle = OpenMutexA(c_dwDesiredAccess, c_initialOwner, c_name);
+        __externalAddressVal(handle) = c_handle;
+        RETURN(handle);
     }
     badArg: ;
 %}.