diff --git a/pkg/apiclient/apiclient_test.go b/pkg/apiclient/apiclient_test.go
index 7bb3b36befdde..b4b35d0b80d48 100644
--- a/pkg/apiclient/apiclient_test.go
+++ b/pkg/apiclient/apiclient_test.go
@@ -7,10 +7,34 @@ import (
 )
 
 func Test_parseHeaders(t *testing.T) {
-	headerString := []string{"foo:", "foo1:bar1", "foo2:bar2:bar2"}
-	headers, err := parseHeaders(headerString)
-	assert.NoError(t, err)
-	assert.Equal(t, headers.Get("foo"), "")
-	assert.Equal(t, headers.Get("foo1"), "bar1")
-	assert.Equal(t, headers.Get("foo2"), "bar2:bar2")
+	t.Run("Header parsed successfully", func(t *testing.T) {
+		headerString := []string{"foo:", "foo1:bar1", "foo2:bar2:bar2"}
+		headers, err := parseHeaders(headerString)
+		assert.NoError(t, err)
+		assert.Equal(t, headers.Get("foo"), "")
+		assert.Equal(t, headers.Get("foo1"), "bar1")
+		assert.Equal(t, headers.Get("foo2"), "bar2:bar2")
+	})
+
+	t.Run("Header parsed error", func(t *testing.T) {
+		headerString := []string{"foo"}
+		_, err := parseHeaders(headerString)
+		assert.ErrorContains(t, err, "additional headers must be colon(:)-separated: foo")
+	})
+}
+
+func Test_parseGRPCHeaders(t *testing.T) {
+	t.Run("Header parsed successfully", func(t *testing.T) {
+		headerStrings := []string{"origin: https://foo.bar", "content-length: 123"}
+		headers, err := parseGRPCHeaders(headerStrings)
+		assert.NoError(t, err)
+		assert.Equal(t, headers.Get("origin"), []string{" https://foo.bar"})
+		assert.Equal(t, headers.Get("content-length"), []string{" 123"})
+	})
+
+	t.Run("Header parsed error", func(t *testing.T) {
+		headerString := []string{"foo"}
+		_, err := parseGRPCHeaders(headerString)
+		assert.ErrorContains(t, err, "additional headers must be colon(:)-separated: foo")
+	})
 }
diff --git a/pkg/apiclient/grpcproxy.go b/pkg/apiclient/grpcproxy.go
index 28af7b62783df..72fea42efee3f 100644
--- a/pkg/apiclient/grpcproxy.go
+++ b/pkg/apiclient/grpcproxy.go
@@ -131,14 +131,14 @@ func (c *client) startGRPCProxy() (*grpc.Server, net.Listener, error) {
 			}
 
 			md, _ := metadata.FromIncomingContext(stream.Context())
+			headersMD, err := parseGRPCHeaders(c.Headers)
 
-			for _, kv := range c.Headers {
-				if len(strings.Split(kv, ":"))%2 == 1 {
-					return fmt.Errorf("additional headers key/values must be separated by a colon(:): %s", kv)
-				}
-				md.Append(strings.Split(kv, ":")[0], strings.Split(kv, ":")[1])
+			if err != nil {
+				return err
 			}
 
+			md = metadata.Join(md, headersMD)
+
 			resp, err := c.executeRequest(fullMethodName, msg, md)
 			if err != nil {
 				return err
@@ -216,3 +216,16 @@ func (c *client) useGRPCProxy() (net.Addr, io.Closer, error) {
 		return nil
 	}), nil
 }
+
+func parseGRPCHeaders(headerStrings []string) (metadata.MD, error) {
+	md := metadata.New(map[string]string{})
+	for _, kv := range headerStrings {
+		i := strings.IndexByte(kv, ':')
+		// zero means meaningless empty header name
+		if i <= 0 {
+			return nil, fmt.Errorf("additional headers must be colon(:)-separated: %s", kv)
+		}
+		md.Append(kv[0:i], kv[i+1:])
+	}
+	return md, nil
+}