diff --git a/overviewer_core/rendermodes.py b/overviewer_core/rendermodes.py
index 6f8d402..30aa718 100644
--- a/overviewer_core/rendermodes.py
+++ b/overviewer_core/rendermodes.py
@@ -212,6 +212,7 @@ class BiomeOverlay(Overlay):
     name = "overlay-biomes"
     options = {
         'biomes' : ('a list of (biome, (r, g, b)) tuples for coloring biomes', None),
+        'alpha'  : ('an integer value between 0 (transparent) and 255 (opaque)', None),
     }
 
 class Hide(RenderPrimitive):
diff --git a/overviewer_core/src/primitives/overlay-biomes.c b/overviewer_core/src/primitives/overlay-biomes.c
index da3e99b..097af13 100644
--- a/overviewer_core/src/primitives/overlay-biomes.c
+++ b/overviewer_core/src/primitives/overlay-biomes.c
@@ -84,9 +84,8 @@ static void get_color(void *data, RenderState *state,
                 *g = biomes[i].g;
                 *b = biomes[i].b;
                 
-                tmp = (128 - y_max + y) * 2 - 40;
-                *a = MIN(MAX(0, tmp), 255);
-                
+                *a = self->parent.color->a;
+
                 max_i = i;
                 break;
             }
@@ -98,6 +97,7 @@ static int
 overlay_biomes_start(void *data, RenderState *state, PyObject *support) {
     PyObject *opt;
     RenderPrimitiveBiomes* self;
+    unsigned char alpha_tmp=0;
 
     /* first, chain up */
     int ret = primitive_overlay.start(data, state, support);
@@ -153,6 +153,14 @@ overlay_biomes_start(void *data, RenderState *state, PyObject *support) {
         self->biomes = default_biomes;
     }
     
+    if (!render_mode_parse_option(support, "alpha", "b", &(alpha_tmp))) {
+        if (PyErr_Occurred()) {
+            PyErr_Clear();
+	    alpha_tmp = 240;
+        }
+
+	self->parent.color->a = alpha_tmp;
+    }
     /* setup custom color */
     self->parent.get_color = get_color;