diff --git a/plugins/input/raster/raster_datasource.cpp b/plugins/input/raster/raster_datasource.cpp
index 110211251..25541857d 100644
--- a/plugins/input/raster/raster_datasource.cpp
+++ b/plugins/input/raster/raster_datasource.cpp
@@ -27,6 +27,7 @@
 // mapnik
 #include <mapnik/debug.hpp>
 #include <mapnik/ctrans.hpp>
+#include <mapnik/image_util.hpp>
 #include <mapnik/image_reader.hpp>
 #include <mapnik/boolean.hpp>
 
@@ -46,9 +47,9 @@ using mapnik::image_reader;
 DATASOURCE_PLUGIN(raster_datasource)
 
 raster_datasource::raster_datasource(parameters const& params)
-    : datasource(params),
-      desc_(*params.get<std::string>("type"), "utf-8"),
-      extent_initialized_(false)
+: datasource(params),
+    desc_(*params.get<std::string>("type"), "utf-8"),
+    extent_initialized_(false)
 {
     MAPNIK_LOG_DEBUG(raster) << "raster_datasource: Initializing...";
 
@@ -65,15 +66,16 @@ raster_datasource::raster_datasource(parameters const& params)
     tile_size_ = *params.get<int>("tile_size", 256);
     tile_stride_ = *params.get<int>("tile_stride", 1);
 
-    format_ = *params.get<std::string>("format","tiff");
+    boost::optional<std::string> format_from_filename = mapnik::type_from_filename(*file);
+    format_ = *params.get<std::string>("format",format_from_filename?(*format_from_filename) : "tiff");
 
     boost::optional<double> lox = params.get<double>("lox");
     boost::optional<double> loy = params.get<double>("loy");
     boost::optional<double> hix = params.get<double>("hix");
     boost::optional<double> hiy = params.get<double>("hiy");
-    
+
     boost::optional<std::string> ext = params.get<std::string>("extent");
-    
+
     if (lox && loy && hix && hiy)
     {
         extent_.init(*lox, *loy, *hix, *hiy);
@@ -88,7 +90,7 @@ raster_datasource::raster_datasource(parameters const& params)
     {
         throw datasource_exception("Raster Plugin: valid <extent> or <lox> <loy> <hix> <hiy> are required");
     }
-    
+
     if (multi_tiles_)
     {
         boost::optional<int> x_width = params.get<int>("x_width");