diff --git a/litex/build/openfpgaloader.py b/litex/build/openfpgaloader.py
index 21e704bf4c..8b41d3093a 100644
--- a/litex/build/openfpgaloader.py
+++ b/litex/build/openfpgaloader.py
@@ -66,7 +66,7 @@ def flash(self, address, data_file, external=False, unprotect_flash=False, verif
 
         # Handle kwargs for specific, less common cases.
         for key, value in kwargs.items():
-            cmd.append(f"--{key}")
+            cmd.append(f"--{key.replace('_', '-')}")
             if value is not None:
                 cmd.append(str(value))