diff --git a/src/tests/test_4015.cc b/src/tests/test_4015.cc
index 3ac3bcde067..dd6ccd9aae6 100644
--- a/src/tests/test_4015.cc
+++ b/src/tests/test_4015.cc
@@ -98,6 +98,7 @@ static void my_parse_args (int argc, char * const argv[]) {
 int test_main(int argc, char * const argv[]) {
     my_parse_args(argc, argv);
 
+    db_env_set_num_bucket_mutexes(32);
     { int chk_r = db_env_create(&env, 0); CKERR(chk_r); }
     { int chk_r = env->set_redzone(env, 0); CKERR(chk_r); }
     { int chk_r = env->set_default_bt_compare(env, my_compare); CKERR(chk_r); }
diff --git a/src/tests/test_groupcommit_count.cc b/src/tests/test_groupcommit_count.cc
index 1358375b218..730e12a870d 100644
--- a/src/tests/test_groupcommit_count.cc
+++ b/src/tests/test_groupcommit_count.cc
@@ -190,6 +190,7 @@ test_main (int argc, char *const argv[]) {
     prev_count=0;
 
     db_env_set_func_fsync(do_fsync);
+    db_env_set_num_bucket_mutexes(32);
 
     {
 	int size=20+strlen(env_path);