diff --git a/t/t5400-send-pack.sh b/t/t5400-send-pack.sh
index 571d620aed..b84618c925 100755
--- a/t/t5400-send-pack.sh
+++ b/t/t5400-send-pack.sh
@@ -288,7 +288,7 @@ test_expect_success 'receive-pack de-dupes .have lines' '
 	$shared .have
 	EOF
 
-	GIT_TRACE_PACKET=$(pwd)/trace GIT_TEST_PROTOCOL_VERSION= \
+	GIT_TRACE_PACKET=$(pwd)/trace GIT_TEST_PROTOCOL_VERSION=0 \
 	    git push \
 		--receive-pack="unset GIT_TRACE_PACKET; git-receive-pack" \
 		fork HEAD:foo &&
diff --git a/t/t5500-fetch-pack.sh b/t/t5500-fetch-pack.sh
index 964930b2d2..baa1a99f45 100755
--- a/t/t5500-fetch-pack.sh
+++ b/t/t5500-fetch-pack.sh
@@ -440,11 +440,12 @@ test_expect_success 'setup tests for the --stdin parameter' '
 '
 
 test_expect_success 'setup fetch refs from cmdline v[12]' '
+	cp -r client client0 &&
 	cp -r client client1 &&
 	cp -r client client2
 '
 
-for version in '' 1 2
+for version in '' 0 1 2
 do
 	test_expect_success "protocol.version=$version fetch refs from cmdline" "
 		(
@@ -638,7 +639,7 @@ test_expect_success 'fetch-pack cannot fetch a raw sha1 that is not advertised a
 	git init client &&
 	# Some protocol versions (e.g. 2) support fetching
 	# unadvertised objects, so restrict this test to v0.
-	test_must_fail env GIT_TEST_PROTOCOL_VERSION= git -C client fetch-pack ../server \
+	test_must_fail env GIT_TEST_PROTOCOL_VERSION=0 git -C client fetch-pack ../server \
 		$(git -C server rev-parse refs/heads/master^) 2>err &&
 	test_i18ngrep "Server does not allow request for unadvertised object" err
 '
diff --git a/t/t5512-ls-remote.sh b/t/t5512-ls-remote.sh
index d7b9f9078f..459d1fcddf 100755
--- a/t/t5512-ls-remote.sh
+++ b/t/t5512-ls-remote.sh
@@ -225,7 +225,7 @@ test_expect_success 'ls-remote --symref' '
 	EOF
 	# Protocol v2 supports sending symrefs for refs other than HEAD, so use
 	# protocol v0 here.
-	GIT_TEST_PROTOCOL_VERSION= git ls-remote --symref >actual &&
+	GIT_TEST_PROTOCOL_VERSION=0 git ls-remote --symref >actual &&
 	test_cmp expect actual
 '
 
@@ -236,7 +236,7 @@ test_expect_success 'ls-remote with filtered symref (refname)' '
 	EOF
 	# Protocol v2 supports sending symrefs for refs other than HEAD, so use
 	# protocol v0 here.
-	GIT_TEST_PROTOCOL_VERSION= git ls-remote --symref . HEAD >actual &&
+	GIT_TEST_PROTOCOL_VERSION=0 git ls-remote --symref . HEAD >actual &&
 	test_cmp expect actual
 '
 
@@ -249,7 +249,7 @@ test_expect_failure 'ls-remote with filtered symref (--heads)' '
 	EOF
 	# Protocol v2 supports sending symrefs for refs other than HEAD, so use
 	# protocol v0 here.
-	GIT_TEST_PROTOCOL_VERSION= git ls-remote --symref --heads . >actual &&
+	GIT_TEST_PROTOCOL_VERSION=0 git ls-remote --symref --heads . >actual &&
 	test_cmp expect actual
 '
 
@@ -260,9 +260,9 @@ test_expect_success 'ls-remote --symref omits filtered-out matches' '
 	EOF
 	# Protocol v2 supports sending symrefs for refs other than HEAD, so use
 	# protocol v0 here.
-	GIT_TEST_PROTOCOL_VERSION= git ls-remote --symref --heads . >actual &&
+	GIT_TEST_PROTOCOL_VERSION=0 git ls-remote --symref --heads . >actual &&
 	test_cmp expect actual &&
-	GIT_TEST_PROTOCOL_VERSION= git ls-remote --symref . "refs/heads/*" >actual &&
+	GIT_TEST_PROTOCOL_VERSION=0 git ls-remote --symref . "refs/heads/*" >actual &&
 	test_cmp expect actual
 '
 
diff --git a/t/t5515-fetch-merge-logic.sh b/t/t5515-fetch-merge-logic.sh
index 961eb35c99..a9a7d50d3e 100755
--- a/t/t5515-fetch-merge-logic.sh
+++ b/t/t5515-fetch-merge-logic.sh
@@ -8,7 +8,8 @@ test_description='Merge logic in fetch'
 
 # NEEDSWORK: If the overspecification of the expected result is reduced, we
 # might be able to run this test in all protocol versions.
-GIT_TEST_PROTOCOL_VERSION=
+GIT_TEST_PROTOCOL_VERSION=0
+export GIT_TEST_PROTOCOL_VERSION
 
 . ./test-lib.sh
 
diff --git a/t/t5516-fetch-push.sh b/t/t5516-fetch-push.sh
index c81ca360ac..f12cbef097 100755
--- a/t/t5516-fetch-push.sh
+++ b/t/t5516-fetch-push.sh
@@ -1151,7 +1151,7 @@ test_expect_success 'fetch exact SHA1' '
 		# unadvertised objects, so restrict this test to v0.
 
 		# fetching the hidden object should fail by default
-		test_must_fail env GIT_TEST_PROTOCOL_VERSION= \
+		test_must_fail env GIT_TEST_PROTOCOL_VERSION=0 \
 			git fetch -v ../testrepo $the_commit:refs/heads/copy 2>err &&
 		test_i18ngrep "Server does not allow request for unadvertised object" err &&
 		test_must_fail git rev-parse --verify refs/heads/copy &&
@@ -1210,7 +1210,7 @@ do
 			cd shallow &&
 			# Some protocol versions (e.g. 2) support fetching
 			# unadvertised objects, so restrict this test to v0.
-			test_must_fail env GIT_TEST_PROTOCOL_VERSION= \
+			test_must_fail env GIT_TEST_PROTOCOL_VERSION=0 \
 				git fetch --depth=1 ../testrepo/.git $SHA1 &&
 			git --git-dir=../testrepo/.git config uploadpack.allowreachablesha1inwant true &&
 			git fetch --depth=1 ../testrepo/.git $SHA1 &&
@@ -1241,9 +1241,9 @@ do
 			cd shallow &&
 			# Some protocol versions (e.g. 2) support fetching
 			# unadvertised objects, so restrict this test to v0.
-			test_must_fail env GIT_TEST_PROTOCOL_VERSION= \
+			test_must_fail env GIT_TEST_PROTOCOL_VERSION=0 \
 				git fetch ../testrepo/.git $SHA1_3 &&
-			test_must_fail env GIT_TEST_PROTOCOL_VERSION= \
+			test_must_fail env GIT_TEST_PROTOCOL_VERSION=0 \
 				git fetch ../testrepo/.git $SHA1_1 &&
 			git --git-dir=../testrepo/.git config uploadpack.allowreachablesha1inwant true &&
 			git fetch ../testrepo/.git $SHA1_1 &&
@@ -1251,7 +1251,7 @@ do
 			test_must_fail git cat-file commit $SHA1_2 &&
 			git fetch ../testrepo/.git $SHA1_2 &&
 			git cat-file commit $SHA1_2 &&
-			test_must_fail env GIT_TEST_PROTOCOL_VERSION= \
+			test_must_fail env GIT_TEST_PROTOCOL_VERSION=0 \
 				git fetch ../testrepo/.git $SHA1_3 2>err &&
 			test_i18ngrep "remote error:.*not our ref.*$SHA1_3\$" err
 		)
@@ -1291,7 +1291,7 @@ test_expect_success 'peeled advertisements are not considered ref tips' '
 	git -C testrepo commit --allow-empty -m two &&
 	git -C testrepo tag -m foo mytag HEAD^ &&
 	oid=$(git -C testrepo rev-parse mytag^{commit}) &&
-	test_must_fail env GIT_TEST_PROTOCOL_VERSION= \
+	test_must_fail env GIT_TEST_PROTOCOL_VERSION=0 \
 		git fetch testrepo $oid 2>err &&
 	test_i18ngrep "Server does not allow request for unadvertised object" err
 '
diff --git a/t/t5539-fetch-http-shallow.sh b/t/t5539-fetch-http-shallow.sh
index b4ad81f006..c0d02dee89 100755
--- a/t/t5539-fetch-http-shallow.sh
+++ b/t/t5539-fetch-http-shallow.sh
@@ -69,7 +69,7 @@ test_expect_success 'no shallow lines after receiving ACK ready' '
 		test_commit new-too &&
 		# NEEDSWORK: If the overspecification of the expected result is reduced, we
 		# might be able to run this test in all protocol versions.
-		GIT_TRACE_PACKET="$TRASH_DIRECTORY/trace" GIT_TEST_PROTOCOL_VERSION= \
+		GIT_TRACE_PACKET="$TRASH_DIRECTORY/trace" GIT_TEST_PROTOCOL_VERSION=0 \
 			git fetch --depth=2 &&
 		grep "fetch-pack< ACK .* ready" ../trace &&
 		! grep "fetch-pack> done" ../trace
diff --git a/t/t5541-http-push-smart.sh b/t/t5541-http-push-smart.sh
index 4c970787b0..23be8ce92d 100755
--- a/t/t5541-http-push-smart.sh
+++ b/t/t5541-http-push-smart.sh
@@ -49,7 +49,7 @@ test_expect_success 'no empty path components' '
 
 	# NEEDSWORK: If the overspecification of the expected result is reduced, we
 	# might be able to run this test in all protocol versions.
-	if test -z "$GIT_TEST_PROTOCOL_VERSION"
+	if test "$GIT_TEST_PROTOCOL_VERSION" = 0
 	then
 		check_access_log exp
 	fi
@@ -135,7 +135,7 @@ EOF
 test_expect_success 'used receive-pack service' '
 	# NEEDSWORK: If the overspecification of the expected result is reduced, we
 	# might be able to run this test in all protocol versions.
-	if test -z "$GIT_TEST_PROTOCOL_VERSION"
+	if test "$GIT_TEST_PROTOCOL_VERSION" = 0
 	then
 		check_access_log exp
 	fi
diff --git a/t/t5551-http-fetch-smart.sh b/t/t5551-http-fetch-smart.sh
index e38e543867..6788aeface 100755
--- a/t/t5551-http-fetch-smart.sh
+++ b/t/t5551-http-fetch-smart.sh
@@ -43,7 +43,7 @@ test_expect_success 'clone http repository' '
 	< Cache-Control: no-cache, max-age=0, must-revalidate
 	< Content-Type: application/x-git-upload-pack-result
 	EOF
-	GIT_TRACE_CURL=true GIT_TEST_PROTOCOL_VERSION= \
+	GIT_TRACE_CURL=true GIT_TEST_PROTOCOL_VERSION=0 \
 		git clone --quiet $HTTPD_URL/smart/repo.git clone 2>err &&
 	test_cmp file clone/file &&
 	tr '\''\015'\'' Q <err |
@@ -84,7 +84,7 @@ test_expect_success 'clone http repository' '
 
 	# NEEDSWORK: If the overspecification of the expected result is reduced, we
 	# might be able to run this test in all protocol versions.
-	if test -z "$GIT_TEST_PROTOCOL_VERSION"
+	if test "$GIT_TEST_PROTOCOL_VERSION" = 0
 	then
 		sed -e "s/^> Accept-Encoding: .*/> Accept-Encoding: ENCODINGS/" \
 				actual >actual.smudged &&
@@ -113,7 +113,7 @@ test_expect_success 'used upload-pack service' '
 
 	# NEEDSWORK: If the overspecification of the expected result is reduced, we
 	# might be able to run this test in all protocol versions.
-	if test -z "$GIT_TEST_PROTOCOL_VERSION"
+	if test "$GIT_TEST_PROTOCOL_VERSION" = 0
 	then
 		check_access_log exp
 	fi
@@ -241,7 +241,7 @@ test_expect_success 'cookies stored in http.cookiefile when http.savecookies set
 
 	# NEEDSWORK: If the overspecification of the expected result is reduced, we
 	# might be able to run this test in all protocol versions.
-	if test -z "$GIT_TEST_PROTOCOL_VERSION"
+	if test "$GIT_TEST_PROTOCOL_VERSION" = 0
 	then
 		tail -3 cookies.txt | sort >cookies_tail.txt &&
 		test_cmp expect_cookies.txt cookies_tail.txt
@@ -336,7 +336,7 @@ test_expect_success 'test allowreachablesha1inwant with unreachable' '
 	git -C test_reachable.git remote add origin "$HTTPD_URL/smart/repo.git" &&
 	# Some protocol versions (e.g. 2) support fetching
 	# unadvertised objects, so restrict this test to v0.
-	test_must_fail env GIT_TEST_PROTOCOL_VERSION= \
+	test_must_fail env GIT_TEST_PROTOCOL_VERSION=0 \
 		git -C test_reachable.git fetch origin "$(git rev-parse HEAD)"
 '
 
@@ -358,7 +358,7 @@ test_expect_success 'test allowanysha1inwant with unreachable' '
 	git -C test_reachable.git remote add origin "$HTTPD_URL/smart/repo.git" &&
 	# Some protocol versions (e.g. 2) support fetching
 	# unadvertised objects, so restrict this test to v0.
-	test_must_fail env GIT_TEST_PROTOCOL_VERSION= \
+	test_must_fail env GIT_TEST_PROTOCOL_VERSION=0 \
 		git -C test_reachable.git fetch origin "$(git rev-parse HEAD)" &&
 
 	git -C "$server" config uploadpack.allowanysha1inwant 1 &&
diff --git a/t/t5552-skipping-fetch-negotiator.sh b/t/t5552-skipping-fetch-negotiator.sh
index f70cbcc9ca..a2a5e0743f 100755
--- a/t/t5552-skipping-fetch-negotiator.sh
+++ b/t/t5552-skipping-fetch-negotiator.sh
@@ -107,7 +107,7 @@ test_expect_success 'use ref advertisement to filter out commits' '
 
 	# The ref advertisement itself is filtered when protocol v2 is used, so
 	# use v0.
-	GIT_TEST_PROTOCOL_VERSION= trace_fetch client origin to_fetch &&
+	GIT_TEST_PROTOCOL_VERSION=0 trace_fetch client origin to_fetch &&
 	have_sent c5 c4^ c2side &&
 	have_not_sent c4 c4^^ c4^^^
 '
diff --git a/t/t5700-protocol-v1.sh b/t/t5700-protocol-v1.sh
index 2571eb90b7..022901b9eb 100755
--- a/t/t5700-protocol-v1.sh
+++ b/t/t5700-protocol-v1.sh
@@ -5,7 +5,8 @@ test_description='test git wire-protocol transition'
 TEST_NO_CREATE_REPO=1
 
 # This is a protocol-specific test.
-GIT_TEST_PROTOCOL_VERSION=
+GIT_TEST_PROTOCOL_VERSION=0
+export GIT_TEST_PROTOCOL_VERSION
 
 . ./test-lib.sh
 
diff --git a/t/t7406-submodule-update.sh b/t/t7406-submodule-update.sh
index 7478f7ab7e..4fb447a143 100755
--- a/t/t7406-submodule-update.sh
+++ b/t/t7406-submodule-update.sh
@@ -960,7 +960,7 @@ test_expect_success 'submodule update clone shallow submodule outside of depth'
 		mv -f .gitmodules.tmp .gitmodules &&
 		# Some protocol versions (e.g. 2) support fetching
 		# unadvertised objects, so restrict this test to v0.
-		test_must_fail env GIT_TEST_PROTOCOL_VERSION= \
+		test_must_fail env GIT_TEST_PROTOCOL_VERSION=0 \
 			git submodule update --init --depth=1 2>actual &&
 		test_i18ngrep "Direct fetching of that commit failed." actual &&
 		git -C ../submodule config uploadpack.allowReachableSHA1InWant true &&
