diff --git a/services/flipcash/src/main/kotlin/com/flipcash/services/internal/domain/UserFlagsMapper.kt b/services/flipcash/src/main/kotlin/com/flipcash/services/internal/domain/UserFlagsMapper.kt
index 0156fce55..c55b96d1d 100644
--- a/services/flipcash/src/main/kotlin/com/flipcash/services/internal/domain/UserFlagsMapper.kt
+++ b/services/flipcash/src/main/kotlin/com/flipcash/services/internal/domain/UserFlagsMapper.kt
@@ -22,7 +22,9 @@ internal class UserFlagsMapper @Inject constructor():
             preferredOnRampProvider = from.preferredOnRampProvider.toDomain().takeIf { it != OnRampProvider.Unknown },
             supportedOnRampProviders = from.supportedOnRampProvidersList.map { it.toDomain() },
             minimumVersion = from.minBuildNumber,
-            billExchangeDataTimeout = from.billExchangeDataTimeout.seconds.toDuration(DurationUnit.SECONDS),
+            billExchangeDataTimeout = if (from.hasBillExchangeDataTimeout()) {
+                from.billExchangeDataTimeout.seconds.toDuration(DurationUnit.SECONDS)
+            } else null,
             newCurrencyPurchaseAmount = Fiat(quarks = from.newCurrencyPurchaseAmount),
             newCurrencyFeeAmount = Fiat(quarks = from.newCurrencyFeeAmount),
             withdrawalFeeAmount = Fiat(quarks = from.withdrawalFeeAmount),
diff --git a/services/flipcash/src/main/kotlin/com/flipcash/services/models/UserFlags.kt b/services/flipcash/src/main/kotlin/com/flipcash/services/models/UserFlags.kt
index 6b4f46e72..fcdac2249 100644
--- a/services/flipcash/src/main/kotlin/com/flipcash/services/models/UserFlags.kt
+++ b/services/flipcash/src/main/kotlin/com/flipcash/services/models/UserFlags.kt
@@ -12,6 +12,9 @@ data class UserFlags(
     val preferredOnRampProvider: OnRampProvider?,
     val supportedOnRampProviders: List<OnRampProvider>,
     val minimumVersion: Int?,
+    // How long a verified exchange rate stays usable for a bill. Absent when the
+    // server hasn't set a timeout (not the same as a zero-length one, which
+    // disables verified exchange data entirely).
     val billExchangeDataTimeout: Duration?,
     val newCurrencyPurchaseAmount: Fiat,
     val newCurrencyFeeAmount: Fiat,
diff --git a/services/flipcash/src/test/kotlin/com/flipcash/services/internal/domain/UserFlagsMapperTest.kt b/services/flipcash/src/test/kotlin/com/flipcash/services/internal/domain/UserFlagsMapperTest.kt
index 12f85c3ed..b48e78de5 100644
--- a/services/flipcash/src/test/kotlin/com/flipcash/services/internal/domain/UserFlagsMapperTest.kt
+++ b/services/flipcash/src/test/kotlin/com/flipcash/services/internal/domain/UserFlagsMapperTest.kt
@@ -116,6 +116,15 @@ class UserFlagsMapperTest {
         assertEquals(30.seconds, result.billExchangeDataTimeout)
     }
 
+    @Test
+    fun `bill exchange data timeout is null when unset, not zero`() {
+        val proto = userFlags { }
+
+        val result = mapper.map(proto)
+
+        assertNull(result.billExchangeDataTimeout)
+    }
+
     @Test
     fun `maps new currency purchase amount`() {
         val proto = userFlags {