diff -Naur tcl8.6.5-orig/win/tclWinInt.h tcl8.6.5/win/tclWinInt.h
--- tcl8.6.5-orig/win/tclWinInt.h	2016-02-25 23:12:38.000000000 +0300
+++ tcl8.6.5/win/tclWinInt.h	2016-03-03 08:47:51.129171100 +0300
@@ -45,7 +45,11 @@
 #endif
 
 #ifdef _WIN64
+# ifdef __USE_MINGW_ANSI_STDIO
+#         define TCL_I_MODIFIER        "I64"
+# else
 #         define TCL_I_MODIFIER        "I"
+# endif
 #else
 #         define TCL_I_MODIFIER        ""
 #endif