diff --git a/test/py.twisted/Makefile.am b/test/py.twisted/Makefile.am
index 5020215..78cde22 100644
--- a/test/py.twisted/Makefile.am
+++ b/test/py.twisted/Makefile.am
@@ -18,6 +18,7 @@
 #
 
 THRIFT = $(top_builddir)/compiler/cpp/thrift
+TRIAL ?= trial
 
 stubs: ../ThriftTest.thrift ../SmallTest.thrift
 	$(THRIFT) --gen py:twisted ../ThriftTest.thrift