diff --git a/winbuild/config.py b/winbuild/config.py
index 1b5d5e380d9..1b5b932102a 100644
--- a/winbuild/config.py
+++ b/winbuild/config.py
@@ -62,17 +62,17 @@
         'version': '8.5.19',
     },
     'tcl-8.6': {
-        'url': SF_MIRROR+'/project/tcl/Tcl/8.6.5/tcl865-src.zip',
-        'filename': PILLOW_DEPENDS_DIR + 'tcl865-src.zip',
-        'hash': 'md5:932e360acb40ec760ebeed659bc893de',
+        'url': SF_MIRROR+'/project/tcl/Tcl/8.6.6/tcl866-src.zip',
+        'filename': PILLOW_DEPENDS_DIR + 'tcl866-src.zip',
+        'hash': 'md5:45dae95abc12a5f8c29dca5baf169a13',
         'dir': '',
     },
     'tk-8.6': {
-        'url': SF_MIRROR+'/project/tcl/Tcl/8.6.5/tk865-src.zip',
-        'filename': PILLOW_DEPENDS_DIR + 'tk865-src.zip',
-        'hash': 'md5:f2f5802a5a3b1f70b906e6930db12089',
+        'url': SF_MIRROR+'/project/tcl/Tcl/8.6.6/tk866-src.zip',
+        'filename': PILLOW_DEPENDS_DIR + 'tk866-src.zip',
+        'hash': 'md5:5004cc0ed2ab820406a36a0c0553b917',
         'dir': '',
-        'version': '8.6.5',
+        'version': '8.6.6',
     },
     'webp': {
         'url': 'http://downloads.webmproject.org/releases/webp/libwebp-0.5.0.tar.gz',