diff --git a/pyopencl/__init__.py b/pyopencl/__init__.py
index 607b8696237460a03566c49463a3042cd2de7fe1..c4a452ed2d159b63d2925fb29dfaee71229696d6 100644
--- a/pyopencl/__init__.py
+++ b/pyopencl/__init__.py
@@ -41,13 +41,16 @@ def _add_functionality():
                 ],
             }
 
-    def to_string(cls, value):
+    def to_string(cls, value, default_format=None):
         for name in dir(cls):
             if (not name.startswith("_") and getattr(cls, name) == value):
                 return name
 
-        raise ValueError("a name for value %d was not found in %s"
-                % (value, cls.__name__))
+        if default_format is None:
+            raise ValueError("a name for value %d was not found in %s"
+                    % (value, cls.__name__))
+        else:
+            return default_format % value
 
     for cls in CONSTANT_CLASSES:
         cls.to_string = classmethod(to_string)
@@ -243,8 +246,10 @@ def _add_functionality():
     # {{{ ImageFormat
     def image_format_repr(self):
         return "ImageFormat(%s, %s)" % (
-                channel_order.to_string(self.channel_order),
-                channel_type.to_string(self.channel_data_type))
+                channel_order.to_string(self.channel_order, 
+                    "<unknown channel order %d>"),
+                channel_type.to_string(self.channel_data_type,
+                    "<unknown channel data type %d>"))
 
     ImageFormat.__repr__ = image_format_repr
     # }}}
diff --git a/src/wrapper/wrap_cl.hpp b/src/wrapper/wrap_cl.hpp
index 233ea32aebc237b837cdee7fb3e5c986e364059f..6acdccbe791df7ea415d56400e69ae99f1b688a2 100644
--- a/src/wrapper/wrap_cl.hpp
+++ b/src/wrapper/wrap_cl.hpp
@@ -1565,17 +1565,15 @@ namespace pyopencl
       cl_mem_flags flags,
       cl_mem_object_type image_type)
   {
-    cl_uint num_image_formats = 1024;
-    std::vector<cl_image_format> formats(num_image_formats);
-    do
-    {
-      if (formats.size() < num_image_formats)
-        formats.resize(num_image_formats);
+    cl_uint num_image_formats;
+    PYOPENCL_CALL_GUARDED(clGetSupportedImageFormats, (
+          ctx.data(), flags, image_type,
+          0, NULL, &num_image_formats));
 
-      PYOPENCL_CALL_GUARDED(clGetSupportedImageFormats, (
-            ctx.data(), flags, image_type,
-            formats.size(), formats.empty( ) ? NULL : &formats.front(), &num_image_formats));
-    } while (formats.size() < num_image_formats);
+    std::vector<cl_image_format> formats(num_image_formats);
+    PYOPENCL_CALL_GUARDED(clGetSupportedImageFormats, (
+          ctx.data(), flags, image_type,
+          formats.size(), formats.empty( ) ? NULL : &formats.front(), NULL));
 
     PYOPENCL_RETURN_VECTOR(cl_image_format, formats);
   }