--- a/src/test/run-make-fulldeps/sysroot-crates-are-unstable/test.py
+++ b/src/test/run-make-fulldeps/sysroot-crates-are-unstable/test.py
@@ -22,6 +22,7 @@
     if to_input is None:
         child = Popen(command, stdout=PIPE, stderr=PIPE)
     else:
+        to_input = to_input.encode("utf-8")
         child = Popen(command, stdout=PIPE, stderr=PIPE, stdin=PIPE)
     stdout, stderr = child.communicate(input=to_input)
     return (convert_to_string(stdout), convert_to_string(stderr))
--- a/src/test/run-make-fulldeps/sysroot-crates-are-unstable/Makefile
+++ b/src/test/run-make-fulldeps/sysroot-crates-are-unstable/Makefile
@@ -1,2 +1,2 @@
 all:
-	python2.7 test.py
+	python3 test.py