diff -ur vigra-1.11.1/vigranumpy/src/core/vigranumpycore.cxx vigra-1.11.1.new/vigranumpy/src/core/vigranumpycore.cxx
--- vigra-1.11.1/vigranumpy/src/core/vigranumpycore.cxx	2017-05-19 16:01:08.000000000 +0100
+++ vigra-1.11.1.new/vigranumpy/src/core/vigranumpycore.cxx	2018-08-23 00:08:42.980416247 +0100
@@ -61,7 +61,7 @@
 	return checksum(data, size);
 #else
 	Py_ssize_t size = 0;
-	char * data = PyUnicode_AsUTF8AndSize(s.ptr(), &size);
+	const char * data = PyUnicode_AsUTF8AndSize(s.ptr(), &size);
 	return checksum(data, size);
 #endif
 }