diff --git a/pkg/unikontainers/unikernels/utils.go b/pkg/unikontainers/unikernels/utils.go
index 5e0886ab2..8f6bf7363 100644
--- a/pkg/unikontainers/unikernels/utils.go
+++ b/pkg/unikontainers/unikernels/utils.go
@@ -16,30 +16,23 @@ package unikernels
 
 import (
 	"fmt"
+	"net"
 	"os"
-	"strconv"
-	"strings"
 )
 
 func subnetMaskToCIDR(subnetMask string) (int, error) {
-	maskParts := strings.Split(subnetMask, ".")
-	if len(maskParts) != 4 {
-		return 0, fmt.Errorf("invalid subnet mask format")
+	ip := net.ParseIP(subnetMask).To4()
+	if ip == nil {
+		return 0, fmt.Errorf("invalid subnet mask format: %s", subnetMask)
 	}
 
-	var cidr int
-	for _, part := range maskParts {
-		val, err := strconv.Atoi(part)
-		if err != nil || val < 0 || val > 255 {
-			return 0, fmt.Errorf("invalid subnet mask value: %s", part)
-		}
-
-		// Convert part to binary and count the number of 1 bits
-		binary := fmt.Sprintf("%08b", val)
-		cidr += strings.Count(binary, "1")
+	mask := net.IPMask(ip)
+	ones, bits := mask.Size()
+	if bits != 32 {
+		return 0, fmt.Errorf("invalid (non-contiguous) subnet mask: %s", subnetMask)
 	}
 
-	return cidr, nil
+	return ones, nil
 }
 
 func createFile(path string, content string) error {
diff --git a/pkg/unikontainers/unikernels/utils_test.go b/pkg/unikontainers/unikernels/utils_test.go
new file mode 100644
index 000000000..8da4fd2d4
--- /dev/null
+++ b/pkg/unikontainers/unikernels/utils_test.go
@@ -0,0 +1,65 @@
+// Copyright (c) 2023-2026, Nubificus LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package unikernels
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSubnetMaskToCIDR(t *testing.T) {
+	tests := []struct {
+		name      string
+		mask      string
+		wantCIDR  int
+		expectErr bool
+	}{
+		// Canonical masks (/0 - /32)
+		{name: "mask /0", mask: "0.0.0.0", wantCIDR: 0, expectErr: false},
+		{name: "mask /1", mask: "128.0.0.0", wantCIDR: 1, expectErr: false},
+		{name: "mask /8", mask: "255.0.0.0", wantCIDR: 8, expectErr: false},
+		{name: "mask /16", mask: "255.255.0.0", wantCIDR: 16, expectErr: false},
+		{name: "mask /24", mask: "255.255.255.0", wantCIDR: 24, expectErr: false},
+		{name: "mask /28", mask: "255.255.255.240", wantCIDR: 28, expectErr: false},
+		{name: "mask /30", mask: "255.255.255.252", wantCIDR: 30, expectErr: false},
+		{name: "mask /32", mask: "255.255.255.255", wantCIDR: 32, expectErr: false},
+
+		// Non-contiguous netmasks (issue #909)
+		{name: "non-contiguous 255.0.255.0", mask: "255.0.255.0", wantCIDR: 0, expectErr: true},
+		{name: "non-contiguous 0.255.255.255", mask: "0.255.255.255", wantCIDR: 0, expectErr: true},
+		{name: "non-contiguous 255.255.1.0", mask: "255.255.1.0", wantCIDR: 0, expectErr: true},
+		{name: "non-contiguous 255.255.255.2", mask: "255.255.255.2", wantCIDR: 0, expectErr: true},
+		{name: "non-contiguous 255.255.255.253", mask: "255.255.255.253", wantCIDR: 0, expectErr: true},
+
+		// Invalid string formats
+		{name: "invalid string", mask: "invalid", wantCIDR: 0, expectErr: true},
+		{name: "missing octet", mask: "255.255.255", wantCIDR: 0, expectErr: true},
+		{name: "out of range octet", mask: "255.255.255.256", wantCIDR: 0, expectErr: true},
+		{name: "too many octets", mask: "255.255.255.0.0", wantCIDR: 0, expectErr: true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cidr, err := subnetMaskToCIDR(tt.mask)
+			if tt.expectErr {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+				assert.Equal(t, tt.wantCIDR, cidr)
+			}
+		})
+	}
+}