diff --git a/quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip85TrustedAssertions/list/tags/ServiceType.kt b/quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip85TrustedAssertions/list/tags/ServiceType.kt
index dafea6d8cc..a894cb1c75 100644
--- a/quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip85TrustedAssertions/list/tags/ServiceType.kt
+++ b/quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip85TrustedAssertions/list/tags/ServiceType.kt
@@ -33,15 +33,16 @@ data class ServiceType(
         ) = "$kind:$type"
 
         fun parse(serviceType: String): ServiceType? {
-            val (kindStr, type) = serviceType.split(":", limit = 2)
-            val kind = kindStr.toIntOrNull() ?: return null
-            return ServiceType(kind, type)
+            val divider = serviceType.indexOf(':')
+            if (divider < 0 || divider == serviceType.length - 1) return null
+            val kind = serviceType.substring(0, divider).toIntOrNull() ?: return null
+            return ServiceType(kind, serviceType.substring(divider + 1))
         }
 
         fun isOfKind(
             serviceType: String,
             kind: String,
-        ) = serviceType.startsWith(kind) && serviceType[kind.length] == ':'
+        ) = serviceType.length > kind.length && serviceType.startsWith(kind) && serviceType[kind.length] == ':'
     }
 }
 
diff --git a/quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/experimental/nip85TrustedAssertions/ServiceTypeParserTest.kt b/quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/experimental/nip85TrustedAssertions/ServiceTypeParserTest.kt
new file mode 100644
index 0000000000..ced9e6b6a9
--- /dev/null
+++ b/quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/experimental/nip85TrustedAssertions/ServiceTypeParserTest.kt
@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.quartz.experimental.nip85TrustedAssertions
+
+import com.vitorpamplona.quartz.nip85TrustedAssertions.list.tags.ServiceType
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertNull
+import kotlin.test.assertTrue
+
+class ServiceTypeParserTest {
+    @Test
+    fun parseValid() {
+        assertEquals(ServiceType(30382, "rank"), ServiceType.parse("30382:rank"))
+    }
+
+    @Test
+    fun parseKeepsColonsInTheType() {
+        assertEquals(ServiceType(30382, "rank:extra"), ServiceType.parse("30382:rank:extra"))
+    }
+
+    @Test
+    fun parseWithoutSeparator() {
+        // a `["client", "nostria"]` tag ends up here. Must not crash.
+        assertNull(ServiceType.parse("client"))
+    }
+
+    @Test
+    fun parseEmpty() {
+        assertNull(ServiceType.parse(""))
+    }
+
+    @Test
+    fun parseWithoutKind() {
+        assertNull(ServiceType.parse(":rank"))
+    }
+
+    @Test
+    fun parseWithoutType() {
+        assertNull(ServiceType.parse("30382:"))
+    }
+
+    @Test
+    fun parseNonNumericKind() {
+        assertNull(ServiceType.parse("client:nostria"))
+    }
+
+    @Test
+    fun isOfKindMatches() {
+        assertTrue(ServiceType.isOfKind("30382:rank", "30382"))
+    }
+
+    @Test
+    fun isOfKindOnPrefixWithoutSeparator() {
+        // "30382" starts with "30382" but has no `:` at that position. Must not crash.
+        assertFalse(ServiceType.isOfKind("30382", "30382"))
+        assertFalse(ServiceType.isOfKind("", ""))
+        assertFalse(ServiceType.isOfKind("303820:rank", "30382"))
+        assertFalse(ServiceType.isOfKind("30383:rank", "30382"))
+    }
+}