diff --git a/src/Cache.cpp b/src/Cache.cpp
index 4213e901..c740cc55 100644
--- a/src/Cache.cpp
+++ b/src/Cache.cpp
@@ -46,12 +46,19 @@ static const std::string_view OLM_ACCOUNT_KEY("olm_account");
 static const std::string_view CACHE_FORMAT_VERSION_KEY("cache_format_version");
 static const std::string_view CURRENT_ONLINE_BACKUP_VERSION("current_online_backup_version");
 
-constexpr size_t MAX_RESTORED_MESSAGES = 30'000;
-
-constexpr auto DB_SIZE    = 32ULL * 1024ULL * 1024ULL * 1024ULL; // 32 GB
 constexpr auto MAX_DBS    = 32384UL;
 constexpr auto BATCH_SIZE = 100;
 
+#if Q_PROCESSOR_WORDSIZE >= 5 // 40-bit or more, up to 2^(8*WORDSIZE) words addressable.
+constexpr auto DB_SIZE                 = 32ULL * 1024ULL * 1024ULL * 1024ULL; // 32 GB
+constexpr size_t MAX_RESTORED_MESSAGES = 30'000;
+#elif Q_PROCESSOR_WORDSIZE == 4 // 32-bit address space limits mmaps
+constexpr auto DB_SIZE                 = 1ULL * 1024ULL * 1024ULL * 1024ULL; // 1 GB
+constexpr size_t MAX_RESTORED_MESSAGES = 5'000;
+#else
+#error Not enough virtual address space for the database on target CPU
+#endif
+
 //! Cache databases and their format.
 //!
 //! Contains UI information for the joined rooms. (i.e name, topic, avatar url etc).