diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 90ea19417bc..b19c3665003 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -266,7 +266,7 @@ struct configured_exclusion {
 static struct oidmap configured_exclusions;
 
 static struct oidset excluded_by_config;
-static int name_hash_version = 1;
+static int name_hash_version = -1;
 
 static void validate_name_hash_version(void)
 {
@@ -4609,6 +4609,9 @@ int cmd_pack_objects(int argc,
 	if (pack_to_stdout || !rev_list_all)
 		write_bitmap_index = 0;
 
+	if (name_hash_version < 0)
+		name_hash_version = (int)git_env_ulong("GIT_TEST_NAME_HASH_VERSION", 1);
+
 	validate_name_hash_version();
 	if (write_bitmap_index && name_hash_version != 1) {
 		warning(_("currently, --write-bitmap-index requires --name-hash-version=1"));
diff --git a/t/README b/t/README
index 8c0319b58e5..e63d2360852 100644
--- a/t/README
+++ b/t/README
@@ -492,6 +492,10 @@ a test and then fails then the whole test run will abort. This can help to make
 sure the expected tests are executed and not silently skipped when their
 dependency breaks or is simply not present in a new environment.
 
+GIT_TEST_NAME_HASH_VERSION=<int>, when set, causes 'git pack-objects' to
+assume '--name-hash-version=<n>'.
+
+
 Naming Tests
 ------------
 
diff --git a/t/t5300-pack-object.sh b/t/t5300-pack-object.sh
index 4270eabe8b7..97fe9e561c6 100755
--- a/t/t5300-pack-object.sh
+++ b/t/t5300-pack-object.sh
@@ -675,15 +675,18 @@ do
 done
 
 test_expect_success 'valid and invalid --name-hash-versions' '
+	sane_unset GIT_TEST_NAME_HASH_VERSION &&
+
 	# Valid values are hard to verify other than "do not fail".
 	# Performance tests will be more valuable to validate these versions.
-	for value in 1 2
+	# Negative values are converted to version 1.
+	for value in -1 1 2
 	do
 		git pack-objects base --all --name-hash-version=$value || return 1
 	done &&
 
 	# Invalid values have clear post-conditions.
-	for value in -1 0 3
+	for value in 0 3
 	do
 		test_must_fail git pack-objects base --all --name-hash-version=$value 2>err &&
 		test_grep "invalid --name-hash-version option" err || return 1
diff --git a/t/t5310-pack-bitmaps.sh b/t/t5310-pack-bitmaps.sh
index 7044c7d7c6d..c30522b57fd 100755
--- a/t/t5310-pack-bitmaps.sh
+++ b/t/t5310-pack-bitmaps.sh
@@ -420,7 +420,10 @@ test_bitmap_cases () {
 			cat >expect <<-\EOF &&
 			error: missing value for '\''pack.preferbitmaptips'\''
 			EOF
-			git repack -adb 2>actual &&
+
+			# Disable name hash version adjustment due to stderr comparison.
+			GIT_TEST_NAME_HASH_VERSION=1 \
+				git repack -adb 2>actual &&
 			test_cmp expect actual
 		)
 	'
diff --git a/t/t5333-pseudo-merge-bitmaps.sh b/t/t5333-pseudo-merge-bitmaps.sh
index eca4a1eb8c6..b1553cbaf7f 100755
--- a/t/t5333-pseudo-merge-bitmaps.sh
+++ b/t/t5333-pseudo-merge-bitmaps.sh
@@ -209,6 +209,10 @@ test_expect_success 'bitmapPseudoMerge.stableThreshold creates stable groups' '
 '
 
 test_expect_success 'out of order thresholds are rejected' '
+	# Disable this option to avoid stderr message
+	GIT_TEST_NAME_HASH_VERSION=1 &&
+	export GIT_TEST_NAME_HASH_VERSION &&
+
 	test_must_fail git \
 		-c bitmapPseudoMerge.test.pattern="refs/*" \
 		-c bitmapPseudoMerge.test.threshold=1.month.ago \
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index 0890b9f61c5..1699c3a3bb8 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -1062,7 +1062,12 @@ test_expect_success 'all boundary commits are excluded' '
 	test_tick &&
 	git merge otherside &&
 	ad=$(git log --no-walk --format=%ad HEAD) &&
-	git bundle create twoside-boundary.bdl main --since="$ad" &&
+
+	# If the a different name hash function is used here, then no delta
+	# pair is found and the bundle does not expand to three objects
+	# when fixing the thin object.
+	GIT_TEST_NAME_HASH_VERSION=1 \
+		git bundle create twoside-boundary.bdl main --since="$ad" &&
 	test_bundle_object_count --thin twoside-boundary.bdl 3
 '
 
diff --git a/t/t6020-bundle-misc.sh b/t/t6020-bundle-misc.sh
index 34b5cd62c20..a1f18ae71f1 100755
--- a/t/t6020-bundle-misc.sh
+++ b/t/t6020-bundle-misc.sh
@@ -247,7 +247,11 @@ test_expect_success 'create bundle with --since option' '
 	EOF
 	test_cmp expect actual &&
 
-	git bundle create since.bdl \
+	# If a different name hash function is used, then one fewer
+	# delta base is found and this counts a different number
+	# of objects after performing --fix-thin.
+	GIT_TEST_NAME_HASH_VERSION=1 \
+		git bundle create since.bdl \
 		--since "Thu Apr 7 15:27:00 2005 -0700" \
 		--all &&
 
diff --git a/t/t7406-submodule-update.sh b/t/t7406-submodule-update.sh
index 0f0c86f9cb2..ebd9941075a 100755
--- a/t/t7406-submodule-update.sh
+++ b/t/t7406-submodule-update.sh
@@ -1094,7 +1094,9 @@ test_expect_success 'submodule update --quiet passes quietness to fetch with a s
 	) &&
 	git clone super4 super5 &&
 	(cd super5 &&
-	 git submodule update --quiet --init --depth=1 submodule3 >out 2>err &&
+	 # This test var can mess with the stderr output checked in this test.
+	 GIT_TEST_NAME_HASH_VERSION=1 \
+		git submodule update --quiet --init --depth=1 submodule3 >out 2>err &&
 	 test_must_be_empty out &&
 	 test_must_be_empty err
 	) &&
diff --git a/t/t7700-repack.sh b/t/t7700-repack.sh
index b9a5759e01d..16861f80c9c 100755
--- a/t/t7700-repack.sh
+++ b/t/t7700-repack.sh
@@ -309,7 +309,10 @@ test_expect_success 'no bitmaps created if .keep files present' '
 	keep=${pack%.pack}.keep &&
 	test_when_finished "rm -f \"\$keep\"" &&
 	>"$keep" &&
-	git -C bare.git repack -ad 2>stderr &&
+
+	# Disable --name-hash-version test due to stderr comparison.
+	GIT_TEST_NAME_HASH_VERSION=1 \
+		git -C bare.git repack -ad 2>stderr &&
 	test_must_be_empty stderr &&
 	find bare.git/objects/pack/ -type f -name "*.bitmap" >actual &&
 	test_must_be_empty actual
@@ -320,7 +323,10 @@ test_expect_success 'auto-bitmaps do not complain if unavailable' '
 	blob=$(test-tool genrandom big $((1024*1024)) |
 	       git -C bare.git hash-object -w --stdin) &&
 	git -C bare.git update-ref refs/tags/big $blob &&
-	git -C bare.git repack -ad 2>stderr &&
+
+	# Disable --name-hash-version test due to stderr comparison.
+	GIT_TEST_NAME_HASH_VERSION=1 \
+		git -C bare.git repack -ad 2>stderr &&
 	test_must_be_empty stderr &&
 	find bare.git/objects/pack -type f -name "*.bitmap" >actual &&
 	test_must_be_empty actual
