diff --git a/dll/win32/msi/upgrade.c b/dll/win32/msi/upgrade.c
index 36d65be8fe9..034d891c1f9 100644
--- a/dll/win32/msi/upgrade.c
+++ b/dll/win32/msi/upgrade.c
@@ -55,45 +55,59 @@ static BOOL check_language(DWORD lang1, LPCWSTR lang2, DWORD attributes)
         return (lang1 == langdword);
 }
 
-static void append_productcode(MSIPACKAGE* package, LPCWSTR action_property,
-                               LPCWSTR productid)
+static BOOL find_product( const WCHAR *list, const WCHAR *product )
 {
-    LPWSTR prop;
-    LPWSTR newprop;
-    DWORD len;
+    const WCHAR *p = list, *q;
+
+    if (!list) return FALSE;
+    for (;;)
+    {
+        while (*p && *p != '{') p++;
+        if (*p != '{') return FALSE;
+        q = p;
+        while (*q && *q != '}') q++;
+        if (*q != '}') return FALSE;
+        q++;
+        if (q - p < strlenW( product )) return FALSE;
+        if (!memcmp( p, product, (q - p) * sizeof(WCHAR) )) return TRUE;
+        p = q + 1;
+        while (*p && *p != ';') p++;
+        if (*p != ';') break;
+    }
+
+    return FALSE;
+}
+
+static void append_productcode( MSIPACKAGE *package, const WCHAR *action_prop, const WCHAR *product )
+{
+    WCHAR *prop, *newprop;
+    DWORD len = 0;
     UINT r;
 
-    prop = msi_dup_property(package->db, action_property );
-    if (prop)
-        len = strlenW(prop);
-    else
-        len = 0;
-
-    /*separator*/
-    len ++;
-
-    len += strlenW(productid);
-
-    /*null*/
-    len++;
-
-    newprop = msi_alloc( len*sizeof(WCHAR) );
+    prop = msi_dup_property( package->db, action_prop );
+    if (find_product( prop, product ))
+    {
+        TRACE( "related product property %s already contains %s\n", debugstr_w(action_prop), debugstr_w(product) );
+        msi_free( prop );
+        return;
+    }
 
+    if (prop) len += strlenW( prop );
+    len += strlenW( product ) + 2;
+    if (!(newprop = msi_alloc( len * sizeof(WCHAR) ))) return;
     if (prop)
     {
-        strcpyW(newprop,prop);
-        strcatW(newprop,szSemiColon);
+        strcpyW( newprop, prop );
+        strcatW( newprop, szSemiColon );
     }
-    else
-        newprop[0] = 0;
-    strcatW(newprop,productid);
+    else newprop[0] = 0;
+    strcatW( newprop, product );
 
-    r = msi_set_property( package->db, action_property, newprop, -1 );
-    if (r == ERROR_SUCCESS && !strcmpW( action_property, szSourceDir ))
+    r = msi_set_property( package->db, action_prop, newprop, -1 );
+    if (r == ERROR_SUCCESS && !strcmpW( action_prop, szSourceDir ))
         msi_reset_source_folders( package );
 
-    TRACE("Found Related Product... %s now %s\n",
-          debugstr_w(action_property), debugstr_w(newprop));
+    TRACE( "related product property %s now %s\n", debugstr_w(action_prop), debugstr_w(newprop) );
 
     msi_free( prop );
     msi_free( newprop );