diff --git a/Makefile b/Makefile
index efb1872c52..327d63217a 100644
--- a/Makefile
+++ b/Makefile
@@ -656,10 +656,10 @@ TEST_BUILTINS_OBJS += test-chmtime.o
 TEST_BUILTINS_OBJS += test-config.o
 TEST_BUILTINS_OBJS += test-ctype.o
 TEST_BUILTINS_OBJS += test-date.o
+TEST_BUILTINS_OBJS += test-delta.o
 TEST_BUILTINS_OBJS += test-lazy-init-name-hash.o
 TEST_BUILTINS_OBJS += test-sha1.o
 
-TEST_PROGRAMS_NEED_X += test-delta
 TEST_PROGRAMS_NEED_X += test-drop-caches
 TEST_PROGRAMS_NEED_X += test-dump-cache-tree
 TEST_PROGRAMS_NEED_X += test-dump-fsmonitor
diff --git a/t/helper/test-delta.c b/t/helper/test-delta.c
index 591730adc4..34c7259248 100644
--- a/t/helper/test-delta.c
+++ b/t/helper/test-delta.c
@@ -8,14 +8,15 @@
  * published by the Free Software Foundation.
  */
 
+#include "test-tool.h"
 #include "git-compat-util.h"
 #include "delta.h"
 #include "cache.h"
 
 static const char usage_str[] =
-	"test-delta (-d|-p) <from_file> <data_file> <out_file>";
+	"test-tool delta (-d|-p) <from_file> <data_file> <out_file>";
 
-int cmd_main(int argc, const char **argv)
+int cmd__delta(int argc, const char **argv)
 {
 	int fd;
 	struct stat st;
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index cae060d492..52d30b80eb 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -11,6 +11,7 @@ static struct test_cmd cmds[] = {
 	{ "config", cmd__config },
 	{ "ctype", cmd__ctype },
 	{ "date", cmd__date },
+	{ "delta", cmd__delta },
 	{ "lazy-init-name-hash", cmd__lazy_init_name_hash },
 	{ "sha1", cmd__sha1 },
 };
diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h
index 31c20bb656..761705e110 100644
--- a/t/helper/test-tool.h
+++ b/t/helper/test-tool.h
@@ -5,6 +5,7 @@ int cmd__chmtime(int argc, const char **argv);
 int cmd__config(int argc, const char **argv);
 int cmd__ctype(int argc, const char **argv);
 int cmd__date(int argc, const char **argv);
+int cmd__delta(int argc, const char **argv);
 int cmd__lazy_init_name_hash(int argc, const char **argv);
 int cmd__sha1(int argc, const char **argv);