diff --git a/js/src/Makefile.in b/js/src/Makefile.in
index 4ac9f48..6ab5582 100644
--- a/js/src/Makefile.in
+++ b/js/src/Makefile.in
@@ -72,7 +72,7 @@ check:: check-style check-masm check-js-msg check-opcode
 
 check-jstests:
 	$(wildcard $(RUN_TEST_PROGRAM)) $(PYTHON) -u $(srcdir)/tests/jstests.py \
-		--no-progress --format=automation --timeout 300 \
+		--no-progress --format=automation --timeout 600 \
 		$(JSTESTS_EXTRA_ARGS) \
 		$(DIST)/bin/$(JS_SHELL_NAME)$(BIN_SUFFIX)