diff --git a/sky_phone/source/server/phone.lua b/sky_phone/source/server/phone.lua
index 6c3f800..02aab46 100644
--- a/sky_phone/source/server/phone.lua
+++ b/sky_phone/source/server/phone.lua
@@ -25,24 +25,25 @@ local function affected_rows(result)
 end
 
 local function reserve_imei()
-    for _ = 1, 20 do
-        local uuid_rows = Sky.Query("SELECT UUID() AS `id`", {})
-        local uuid = uuid_rows[1] and uuid_rows[1].id
+    local imei = SkyPhoneImei.Reserve(function()
+        local rows = Sky.Query("SELECT UUID() AS `id`", {})
+        local uuid = rows[1] and rows[1].id
         if type(uuid) ~= "string" then
             error("[sky_phone] Database did not generate entropy for an IMEI.")
         end
-
-        local imei = SkyPhoneImei.FromEntropy(uuid)
+        return uuid
+    end, function(candidate)
         local result = Sky.Query([[
             INSERT IGNORE INTO `sky_phone_devices` (`imei`, `device_name`)
             VALUES (?, ?)
-        ]], { imei, Config.Phone.DeviceName })
-        if affected_rows(result) > 0 then
-            return imei
-        end
-    end
+        ]], { candidate, Config.Phone.DeviceName })
+        return affected_rows(result) > 0
+    end)
 
-    error("[sky_phone] Could not generate a unique IMEI after 20 attempts.")
+    if not imei then
+        error("[sky_phone] Could not generate a unique IMEI after 20 attempts.")
+    end
+    return imei
 end
 
 local function find_device_slots(source, imei)
diff --git a/sky_phone/source/shared/imei.lua b/sky_phone/source/shared/imei.lua
index 95b8fe1..54c0a57 100644
--- a/sky_phone/source/shared/imei.lua
+++ b/sky_phone/source/shared/imei.lua
@@ -45,3 +45,14 @@ function SkyPhoneImei.IsValid(value)
     end
     return value:sub(15, 15) == SkyPhoneImei.CheckDigit(value:sub(1, 14))
 end
+
+function SkyPhoneImei.Reserve(entropy_factory, reserve)
+    for _ = 1, 20 do
+        local imei = SkyPhoneImei.FromEntropy(entropy_factory())
+        if imei and reserve(imei) then
+            return imei
+        end
+    end
+
+    return nil
+end
diff --git a/tests/imei.lua b/tests/imei.lua
index 56df8bc..317bafa 100644
--- a/tests/imei.lua
+++ b/tests/imei.lua
@@ -7,4 +7,20 @@ assert(SkyPhoneImei.IsValid(imei), "generated IMEI must pass its check digit")
 assert(not SkyPhoneImei.IsValid(imei:sub(1, 14) .. tostring((tonumber(imei:sub(15, 15)) + 1) % 10)), "invalid check digit must fail")
 assert(not SkyPhoneImei.IsValid("123"), "short IMEI must fail")
 
+local entropy = {
+    "550e8400-e29b-41d4-a716-446655440000",
+    "6ba7b810-9dad-11d1-80b4-00c04fd430c8",
+}
+local entropy_index = 0
+local reserve_attempts = 0
+local reserved = SkyPhoneImei.Reserve(function()
+    entropy_index = entropy_index + 1
+    return entropy[entropy_index]
+end, function()
+    reserve_attempts = reserve_attempts + 1
+    return reserve_attempts == 2
+end)
+assert(reserve_attempts == 2, "IMEI reservation must retry database collisions")
+assert(reserved == SkyPhoneImei.FromEntropy(entropy[2]), "IMEI reservation must return the accepted candidate")
+
 print("IMEI tests passed")