diff --git a/src/main/kotlin/com/featurevisor/sdk/DatafileReader.kt b/src/main/kotlin/com/featurevisor/sdk/DatafileReader.kt
index 7834b77..eef4c77 100644
--- a/src/main/kotlin/com/featurevisor/sdk/DatafileReader.kt
+++ b/src/main/kotlin/com/featurevisor/sdk/DatafileReader.kt
@@ -6,6 +6,7 @@ import com.featurevisor.types.DatafileContent
 import com.featurevisor.types.Feature
 import com.featurevisor.types.FeatureKey
 import com.featurevisor.types.Segment
+import com.featurevisor.types.SegmentKey
 
 class DatafileReader constructor(
     datafileJson: DatafileContent,
@@ -33,7 +34,7 @@ class DatafileReader constructor(
         return attributes.find { attribute -> attribute.key == attributeKey }
     }
 
-    fun getSegment(segmentKey: String): Segment? {
+    fun getSegment(segmentKey: SegmentKey): Segment? {
         return segments.find { segment -> segment.key == segmentKey }
     }
 
diff --git a/src/main/kotlin/com/featurevisor/types/Types.kt b/src/main/kotlin/com/featurevisor/types/Types.kt
index 862f296..ea1d9f8 100644
--- a/src/main/kotlin/com/featurevisor/types/Types.kt
+++ b/src/main/kotlin/com/featurevisor/types/Types.kt
@@ -186,7 +186,7 @@ data class SegmentAssertion(
 )
 
 data class TestSegment(
-    val key: String,
+    val key: SegmentKey,
     val assertions: List<SegmentAssertion>,
 )
 
@@ -238,10 +238,12 @@ sealed class ConditionValue {
     data class DateTimeValue(val value: LocalDate) : ConditionValue()
 }
 
+typealias SegmentKey = String
+
 @Serializable
 data class Segment(
     val archived: Boolean? = null,
-    val key: String,
+    val key: SegmentKey,
     val conditions: Condition,
 )
 
@@ -259,7 +261,7 @@ data class NotGroupSegment(
 
 @Serializable(with = GroupSegmentSerializer::class)
 sealed class GroupSegment {
-    data class Plain(val segment: String) : GroupSegment()
+    data class Plain(val segment: SegmentKey) : GroupSegment()
     data class Multiple(val segments: List<GroupSegment>) : GroupSegment()
     data class And(val segment: AndGroupSegment) : GroupSegment()
     data class Or(val segment: OrGroupSegment) : GroupSegment()