diff -u -r vigra-1.11.1/vigranumpy/src/core/vigranumpycore.cxx vigra-1.11.1-py3.7/vigranumpy/src/core/vigranumpycore.cxx
--- vigra-1.11.1/vigranumpy/src/core/vigranumpycore.cxx	2017-05-19 17:01:08.000000000 +0200
+++ vigra-1.11.1-py3.7/vigranumpy/src/core/vigranumpycore.cxx	2018-07-29 18:29:46.514547076 +0200
@@ -59,10 +59,14 @@
 	Py_ssize_t size = PyUnicode_GET_DATA_SIZE(s.ptr());
 	const char * data = PyUnicode_AS_DATA(s.ptr());
 	return checksum(data, size);
-#else
+#elif (PY_MAJOR_VERSION == 3) && (PY_MINOR_VERSION < 7)
 	Py_ssize_t size = 0;
 	char * data = PyUnicode_AsUTF8AndSize(s.ptr(), &size);
 	return checksum(data, size);
+#else
+	Py_ssize_t size = 0;
+	const char * data = PyUnicode_AsUTF8AndSize(s.ptr(), &size);
+	return checksum(data, size);
 #endif
 }