diff --git a/ext/bigdecimal/bigdecimal.c b/ext/bigdecimal/bigdecimal.c
index 1e6de0e2db..e544bc7df2 100644
--- a/ext/bigdecimal/bigdecimal.c
+++ b/ext/bigdecimal/bigdecimal.c
@@ -2830,7 +2830,7 @@ VpNewVarArg(int argc, VALUE *argv)
 }
 
 /* call-seq:
- *   BigDecimal(initial, digits, exception: true)
+ *   BigDecimal(initial, digits=0, exception: true)
  *
  * Create a new BigDecimal object.
  *