diff --git a/src/init.cpp b/src/init.cpp
index d619cb4121..1e2ffe48e2 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -862,6 +862,11 @@ bool AppInit2(boost::thread_group& threadGroup)
                     break;
                 }
 
+                // If the loaded chain has a wrong genesis, bail out immediately
+                // (we're likely using a testnet datadir, or the other way around).
+                if (!mapBlockIndex.empty() && pindexGenesisBlock == NULL)
+                    return InitError(_("Incorrect or no genesis block found. Wrong datadir for network?"));
+
                 // Initialize the block index (no-op if non-empty database was already loaded)
                 if (!InitBlockIndex()) {
                     strLoadError = _("Error initializing block database");