From 2ac345fd33678a46bd4e9d2c848e7122aeac1bce Mon Sep 17 00:00:00 2001
From: Brad Davidson <brad.davidson@rancher.com>
Date: Tue, 11 Aug 2026 00:32:44 +0000
Subject: [PATCH 1/2] Do not drop OS version when constructing build options

Signed-off-by: Brad Davidson <brad.davidson@rancher.com>
---
 build/opt.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/build/opt.go b/build/opt.go
index a4535e679ac1..3919bd9681e7 100644
--- a/build/opt.go
+++ b/build/opt.go
@@ -580,7 +580,7 @@ func toSolveOpt(ctx context.Context, np *noderesolver.ResolvedNode, multiDriver
 	if len(opt.Platforms) != 0 {
 		pp := make([]string, len(opt.Platforms))
 		for i, p := range opt.Platforms {
-			pp[i] = platforms.Format(p)
+			pp[i] = platforms.FormatAll(p)
 		}
 		if len(pp) > 1 && !nodeDriver.Features(ctx)[driver.MultiPlatform] {
 			return nil, nil, notSupported(driver.MultiPlatform, nodeDriver, "https://docs.docker.com/go/build-multi-platform/")

From 0ea630200b54db15b5c7b912c274c300df5efca2 Mon Sep 17 00:00:00 2001
From: CrazyMax <1951866+crazy-max@users.noreply.github.com>
Date: Tue, 11 Aug 2026 15:31:34 +0200
Subject: [PATCH 2/2] test: integration coverage for OS version platforms

Signed-off-by: CrazyMax <1951866+crazy-max@users.noreply.github.com>
---
 tests/build.go | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/tests/build.go b/tests/build.go
index 63fec7d1fd5b..1b8c7a2504e3 100644
--- a/tests/build.go
+++ b/tests/build.go
@@ -78,6 +78,7 @@ var buildTests = []func(t *testing.T, sb integration.Sandbox){
 	testBuildCacheExportNotSupported,
 	testBuildOCIExportNotSupported,
 	testBuildMultiPlatform,
+	testBuildTargetPlatformOSVersion,
 	testDockerHostGateway,
 	testBuildNetworkModeBridge,
 	testBuildShmSize,
@@ -1006,6 +1007,23 @@ func testBuildMultiPlatform(t *testing.T, sb integration.Sandbox) {
 	}
 }
 
+func testBuildTargetPlatformOSVersion(t *testing.T, sb integration.Sandbox) {
+	skipNoCompatBuildKit(t, sb, ">= 0.19.0-0", "platform OS version")
+	integration.SkipOnPlatform(t, "windows")
+
+	dockerfile := []byte(`
+FROM --platform=$BUILDPLATFORM busybox:latest
+ARG TARGETPLATFORM
+ARG TARGETOSVERSION
+RUN test "$TARGETPLATFORM" = "windows(10.0.17763)/amd64"
+RUN test "$TARGETOSVERSION" = "10.0.17763"
+`)
+	dir := tmpdir(t, fstest.CreateFile("Dockerfile", dockerfile, 0o600))
+
+	out, err := buildCmd(sb, withArgs("--platform=windows(10.0.17763)/amd64", "--output=type=cacheonly", dir))
+	require.NoError(t, err, string(out))
+}
+
 func testDockerHostGateway(t *testing.T, sb integration.Sandbox) {
 	dockerfile := []byte(`
 FROM busybox