Index: binaries/data/mods/public/maps/random/african_plains.js
===================================================================
--- binaries/data/mods/public/maps/random/african_plains.js
+++ binaries/data/mods/public/maps/random/african_plains.js
@@ -2,12 +2,10 @@
 Engine.LoadLibrary("rmgen-common");
 Engine.LoadLibrary("rmbiome");
 
-if (g_MapSettings.Biome)
-	setSelectedBiome();
-else
-	setBiome("generic/savanna");
 
+setSelectedBiome({fallback: "generic/savanna"});
 
+
 // Pick some biome defaults and overload a few settings.
 const tPrimary = g_Terrains.mainTerrain;
 const tForestFloor = g_Terrains.tier3Terrain;
Index: binaries/data/mods/public/maps/random/fields_of_meroe.js
===================================================================
--- binaries/data/mods/public/maps/random/fields_of_meroe.js
+++ binaries/data/mods/public/maps/random/fields_of_meroe.js
@@ -2,10 +2,7 @@
 Engine.LoadLibrary("rmgen-common");
 Engine.LoadLibrary("rmbiome");
 
-if (g_MapSettings.Biome)
-	setSelectedBiome();
-else
-	setBiome("fields_of_meroe/dry");
+setSelectedBiome({fallback: "fields_of_meroe/dry"});
 
 const tMainDirt = g_Terrains.mainDirt;
 const tSecondaryDirt = g_Terrains.secondaryDirt;
Index: binaries/data/mods/public/maps/random/gulf_of_bothnia.js
===================================================================
--- binaries/data/mods/public/maps/random/gulf_of_bothnia.js
+++ binaries/data/mods/public/maps/random/gulf_of_bothnia.js
@@ -4,11 +4,7 @@
 
 TILE_CENTERED_HEIGHT_MAP = true;
 
-if (g_MapSettings.Biome)
-	setSelectedBiome();
-else
-	// TODO: Replace ugly default for atlas by a dropdown
-	setBiome("gulf_of_bothnia/winter");
+setSelectedBiome({fallback: "gulf_of_bothnia/winter"});
 
 const isLakeFrozen = g_Environment.Water.Frozen;
 
Index: binaries/data/mods/public/maps/random/neareastern_badlands.js
===================================================================
--- binaries/data/mods/public/maps/random/neareastern_badlands.js
+++ binaries/data/mods/public/maps/random/neareastern_badlands.js
@@ -2,10 +2,7 @@
 Engine.LoadLibrary("rmgen-common");
 Engine.LoadLibrary("rmbiome");
 
-if (g_MapSettings.Biome)
-	setSelectedBiome();
-else
-	setBiome("generic/sahara");
+setSelectedBiome({fallback: "generic/sahara"});
 
 
 const tPrimary = g_Terrains.mainTerrain;
Index: binaries/data/mods/public/maps/random/persian_highlands.js
===================================================================
--- binaries/data/mods/public/maps/random/persian_highlands.js
+++ binaries/data/mods/public/maps/random/persian_highlands.js
@@ -2,11 +2,7 @@
 Engine.LoadLibrary("rmgen-common");
 Engine.LoadLibrary("rmbiome");
 
-if (g_MapSettings.Biome)
-	setSelectedBiome();
-else
-	// TODO: Replace ugly default for atlas by a dropdown
-	setBiome("persian_highlands/summer");
+setSelectedBiome({fallback: "persian_highlands/summer"});
 
 const tDirtMain = g_Terrains.mainTerrain;
 const tCity = g_Terrains.road;
Index: binaries/data/mods/public/maps/random/rmbiome/randombiome.js
===================================================================
--- binaries/data/mods/public/maps/random/rmbiome/randombiome.js
+++ binaries/data/mods/public/maps/random/rmbiome/randombiome.js
@@ -11,10 +11,36 @@
 	return g_BiomeID;
 }
 
-function setSelectedBiome()
+/**
+ * Get the file path for a biome.
+ * @param {string} biomeID - The biome ID.
+ * @returns {string} - The file path (tested for existance).
+ */
+function getBiomeFilePath(biomeID)
 {
+	const path = "maps/random/rmbiome/" + biomeID + ".json";
+	if (!Engine.FileExists(path))
+	{
+		error("Could not find biome file '" + biomeID + "'");
+		return;
+	}
+	return path;
+}
+
+/**
+ * Sets the selected biome.
+ * @param {Object} arg - optional argument.
+ * @param {string} arg.fallback - The ID of the fallback biome.
+ */
+function setSelectedBiome(arg)
+{
 	// TODO: Replace ugly default for atlas by a dropdown
-	setBiome(g_MapSettings.Biome || "generic/alpine");
+
+	const  fallback = arg?.fallback || "generic/alpine"
+	// We don't have an automated way to test maps in atlas,
+	// so we make sure that the fallback is valid here.
+	const unread = getBiomeFilePath(fallback);
+	setBiome(g_MapSettings.Biome || fallback);
 }
 
 function setBiome(biomeID)
@@ -42,14 +68,8 @@
  */
 function loadBiomeFile(file)
 {
-	const path = "maps/random/rmbiome/" + file + ".json";
 
-	if (!Engine.FileExists(path))
-	{
-		error("Could not load biome file '" + file + "'");
-		return;
-	}
-
+	const path = getBiomeFilePath(file);
 	const biome = Engine.ReadJSONFile(path);
 
 	const copyProperties = (from, to) => {