Index: Modules/_tkinter.c
===================================================================
--- Modules/_tkinter.c	(revision 63812)
+++ Modules/_tkinter.c	(working copy)
@@ -1123,7 +1123,7 @@
 		Tcl_DecrRefCount(value);
 	} else {
 		const char *s = Tcl_GetStringResult(self->interp);
-		const char *p = s;
+		const char *p = strchr(s, '\0');
 
 		res = PyUnicode_FromStringAndSize(s, (int)(p-s));
 	}