diff --git a/cli/command/image/build/context.go b/cli/command/image/build/context.go
index 747c23c7e0..fc1e7b64d4 100644
--- a/cli/command/image/build/context.go
+++ b/cli/command/image/build/context.go
@@ -155,6 +155,9 @@ func GetContextFromReader(rc io.ReadCloser, dockerfileName string) (out io.ReadC
 	if dockerfileName == "-" {
 		return nil, "", errors.New("build context is not an archive")
 	}
+	if dockerfileName != "" {
+		return nil, "", errors.New("ambiguous Dockerfile source: both stdin and flag correspond to Dockerfiles")
+	}
 
 	dockerfileDir, err := WriteTempDockerfile(rc)
 	if err != nil {
diff --git a/cli/command/image/build/context_test.go b/cli/command/image/build/context_test.go
index 15686e0be4..63cfaa0e12 100644
--- a/cli/command/image/build/context_test.go
+++ b/cli/command/image/build/context_test.go
@@ -152,6 +152,13 @@ func TestGetContextFromReaderString(t *testing.T) {
 	}
 }
 
+func TestGetContextFromReaderStringConflict(t *testing.T) {
+	rdr, relDockerfile, err := GetContextFromReader(io.NopCloser(strings.NewReader(dockerfileContents)), "custom.Dockerfile")
+	assert.Check(t, is.Equal(rdr, nil))
+	assert.Check(t, is.Equal(relDockerfile, ""))
+	assert.Check(t, is.ErrorContains(err, "ambiguous Dockerfile source: both stdin and flag correspond to Dockerfiles"))
+}
+
 func TestGetContextFromReaderTar(t *testing.T) {
 	contextDir := createTestTempDir(t)
 	createTestTempFile(t, contextDir, DefaultDockerfileName, dockerfileContents)