https://github.com/eserte/perl-tk/issues/106#issuecomment-3119122513

--- Tk-804.036/pTk/mTk/generic/tkCanvText.c.orig
+++ Tk-804.036/pTk/mTk/generic/tkCanvText.c
@@ -1250,7 +1250,7 @@
 	goto doxy;
     }
 
-    string = Tcl_GetStringFromObj(obj, &length);
+    string = Tcl_GetStringFromObj(obj, NULL);
     c = string[0];
     length = strlen(string);