diff --git a/migen/build/generic_programmer.py b/migen/build/generic_programmer.py
index 82a1ebe07..da49857c9 100644
--- a/migen/build/generic_programmer.py
+++ b/migen/build/generic_programmer.py
@@ -18,7 +18,11 @@ def find_flash_proxy(self):
             fullname = os.path.join(fulldir, self.flash_proxy_basename)
             if os.path.exists(fullname):
                 return fullname
-        raise OSError("Failed to find flash proxy bitstream")
+        raise OSError(
+            "Failed to find flash proxy bitstream {}, searched:\n"
+            "    {}\n".format(
+                self.flash_proxy_basename,
+                "\n    ".join(self.flash_proxy_dirs)))
 
     # must be overloaded by specific programmer
     def load_bitstream(self, bitstream_file):