diff --git a/t/helper/test-hash.c b/t/helper/test-hash.c
index 45d829c908f..d0ee668df95 100644
--- a/t/helper/test-hash.c
+++ b/t/helper/test-hash.c
@@ -1,7 +1,7 @@
 #include "test-tool.h"
 #include "hex.h"
 
-int cmd_hash_impl(int ac, const char **av, int algo)
+int cmd_hash_impl(int ac, const char **av, int algo, int unsafe)
 {
 	git_hash_ctx ctx;
 	unsigned char hash[GIT_MAX_HEXSZ];
@@ -27,7 +27,10 @@ int cmd_hash_impl(int ac, const char **av, int algo)
 			die("OOPS");
 	}
 
-	algop->init_fn(&ctx);
+	if (unsafe)
+		algop->unsafe_init_fn(&ctx);
+	else
+		algop->init_fn(&ctx);
 
 	while (1) {
 		ssize_t sz, this_sz;
@@ -46,9 +49,15 @@ int cmd_hash_impl(int ac, const char **av, int algo)
 		}
 		if (this_sz == 0)
 			break;
-		algop->update_fn(&ctx, buffer, this_sz);
+		if (unsafe)
+			algop->unsafe_update_fn(&ctx, buffer, this_sz);
+		else
+			algop->update_fn(&ctx, buffer, this_sz);
 	}
-	algop->final_fn(hash, &ctx);
+	if (unsafe)
+		algop->unsafe_final_fn(hash, &ctx);
+	else
+		algop->final_fn(hash, &ctx);
 
 	if (binary)
 		fwrite(hash, 1, algop->rawsz, stdout);
diff --git a/t/helper/test-sha1.c b/t/helper/test-sha1.c
index e60d000c039..349540c4df8 100644
--- a/t/helper/test-sha1.c
+++ b/t/helper/test-sha1.c
@@ -3,7 +3,7 @@
 
 int cmd__sha1(int ac, const char **av)
 {
-	return cmd_hash_impl(ac, av, GIT_HASH_SHA1);
+	return cmd_hash_impl(ac, av, GIT_HASH_SHA1, 0);
 }
 
 int cmd__sha1_is_sha1dc(int argc UNUSED, const char **argv UNUSED)
@@ -13,3 +13,8 @@ int cmd__sha1_is_sha1dc(int argc UNUSED, const char **argv UNUSED)
 #endif
 	return 1;
 }
+
+int cmd__sha1_unsafe(int ac, const char **av)
+{
+	return cmd_hash_impl(ac, av, GIT_HASH_SHA1, 1);
+}
diff --git a/t/helper/test-sha1.sh b/t/helper/test-sha1.sh
index 84594885c70..bf387d3db14 100755
--- a/t/helper/test-sha1.sh
+++ b/t/helper/test-sha1.sh
@@ -3,25 +3,31 @@
 dd if=/dev/zero bs=1048576 count=100 2>/dev/null |
 /usr/bin/time t/helper/test-tool sha1 >/dev/null
 
+dd if=/dev/zero bs=1048576 count=100 2>/dev/null |
+/usr/bin/time t/helper/test-tool sha1-unsafe >/dev/null
+
 while read expect cnt pfx
 do
 	case "$expect" in '#'*) continue ;; esac
-	actual=$(
-		{
-			test -z "$pfx" || echo "$pfx"
-			dd if=/dev/zero bs=1048576 count=$cnt 2>/dev/null |
-			perl -pe 'y/\000/g/'
-		} | ./t/helper/test-tool sha1 $cnt
-	)
-	if test "$expect" = "$actual"
-	then
-		echo "OK: $expect $cnt $pfx"
-	else
-		echo >&2 "OOPS: $cnt"
-		echo >&2 "expect: $expect"
-		echo >&2 "actual: $actual"
-		exit 1
-	fi
+	for sha1 in sha1 sha1-unsafe
+	do
+		actual=$(
+			{
+				test -z "$pfx" || echo "$pfx"
+				dd if=/dev/zero bs=1048576 count=$cnt 2>/dev/null |
+				perl -pe 'y/\000/g/'
+			} | ./t/helper/test-tool $sha1 $cnt
+		)
+		if test "$expect" = "$actual"
+		then
+			echo "OK ($sha1): $expect $cnt $pfx"
+		else
+			echo >&2 "OOPS ($sha1): $cnt"
+			echo >&2 "expect ($sha1): $expect"
+			echo >&2 "actual ($sha1): $actual"
+			exit 1
+		fi
+	done
 done <<EOF
 da39a3ee5e6b4b0d3255bfef95601890afd80709 0
 3f786850e387550fdab836ed7e6dc881de23001b 0 a
diff --git a/t/helper/test-sha256.c b/t/helper/test-sha256.c
index 2fb20438f3c..7fd0aa1fcd3 100644
--- a/t/helper/test-sha256.c
+++ b/t/helper/test-sha256.c
@@ -3,5 +3,5 @@
 
 int cmd__sha256(int ac, const char **av)
 {
-	return cmd_hash_impl(ac, av, GIT_HASH_SHA256);
+	return cmd_hash_impl(ac, av, GIT_HASH_SHA256, 0);
 }
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index 4a7aa993ba9..958452ef12e 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -70,6 +70,7 @@ static struct test_cmd cmds[] = {
 	{ "serve-v2", cmd__serve_v2 },
 	{ "sha1", cmd__sha1 },
 	{ "sha1-is-sha1dc", cmd__sha1_is_sha1dc },
+	{ "sha1-unsafe", cmd__sha1_unsafe },
 	{ "sha256", cmd__sha256 },
 	{ "sigchain", cmd__sigchain },
 	{ "simple-ipc", cmd__simple_ipc },
diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h
index 21802ac27da..24149edd414 100644
--- a/t/helper/test-tool.h
+++ b/t/helper/test-tool.h
@@ -63,6 +63,7 @@ int cmd__scrap_cache_tree(int argc, const char **argv);
 int cmd__serve_v2(int argc, const char **argv);
 int cmd__sha1(int argc, const char **argv);
 int cmd__sha1_is_sha1dc(int argc, const char **argv);
+int cmd__sha1_unsafe(int argc, const char **argv);
 int cmd__sha256(int argc, const char **argv);
 int cmd__sigchain(int argc, const char **argv);
 int cmd__simple_ipc(int argc, const char **argv);
@@ -81,6 +82,6 @@ int cmd__windows_named_pipe(int argc, const char **argv);
 #endif
 int cmd__write_cache(int argc, const char **argv);
 
-int cmd_hash_impl(int ac, const char **av, int algo);
+int cmd_hash_impl(int ac, const char **av, int algo, int unsafe);
 
 #endif
