diff --git a/build/opt.go b/build/opt.go
index f7522fe87edd..ed9ca5a02ed3 100644
--- a/build/opt.go
+++ b/build/opt.go
@@ -298,7 +298,11 @@ func toSolveOpt(ctx context.Context, np *noderesolver.ResolvedNode, multiDriver
 	}
 
 	if v, ok := opt.BuildArgs["BUILDKIT_SYNTAX"]; ok {
-		p := strings.SplitN(strings.TrimSpace(v), " ", 2)
+		cmdline := strings.TrimSpace(v)
+		if cmdline == "" {
+			return nil, nil, errors.Errorf("empty BUILDKIT_SYNTAX build-arg is invalid, use --build-arg BUILDKIT_SYNTAX without '=' for optional behavior")
+		}
+		p := strings.SplitN(cmdline, " ", 2)
 		so.Frontend = "gateway.v0"
 		so.FrontendAttrs["source"] = p[0]
 		so.FrontendAttrs["cmdline"] = v
diff --git a/tests/build.go b/tests/build.go
index 5cab893297a6..6412d2428473 100644
--- a/tests/build.go
+++ b/tests/build.go
@@ -62,6 +62,7 @@ var buildTests = []func(t *testing.T, sb integration.Sandbox){
 	testBuildProgress,
 	testBuildAnnotations,
 	testBuildBuildArgNoKey,
+	testBuildBuildKitSyntaxEmpty,
 	testBuildLabelNoKey,
 	testBuildCacheExportNotSupported,
 	testBuildOCIExportNotSupported,
@@ -759,6 +760,14 @@ func testBuildBuildArgNoKey(t *testing.T, sb integration.Sandbox) {
 	require.Equal(t, `ERROR: invalid key-value pair "=TEST_STRING": empty key`, strings.TrimSpace(string(out)))
 }
 
+func testBuildBuildKitSyntaxEmpty(t *testing.T, sb integration.Sandbox) {
+	dir := createTestProject(t)
+	cmd := buildxCmd(sb, withArgs("build", "--build-arg", "BUILDKIT_SYNTAX=", dir))
+	out, err := cmd.CombinedOutput()
+	require.Error(t, err, string(out))
+	require.Contains(t, string(out), `empty BUILDKIT_SYNTAX build-arg is invalid, use --build-arg BUILDKIT_SYNTAX without '=' for optional behavior`)
+}
+
 func testBuildLabelNoKey(t *testing.T, sb integration.Sandbox) {
 	dir := createTestProject(t)
 	cmd := buildxCmd(sb, withArgs("build", "--label", "=TEST_STRING", dir))