diff --git a/mlir/docs/LangRef.md b/mlir/docs/LangRef.md
--- a/mlir/docs/LangRef.md
+++ b/mlir/docs/LangRef.md
@@ -241,7 +241,8 @@
 ```
 operation         ::= op-result-list? (generic-operation | custom-operation)
                       trailing-location?
-generic-operation ::= string-literal '(' ssa-use-list? ')' attribute-dict?
+generic-operation ::= string-literal `(` ssa-use-list? `)`
+                      (`(` region-list `)`)? attribute-dict?
                       `:` function-type
 custom-operation  ::= bare-id custom-operation-format
 op-result-list    ::= op-result (`,` op-result)* `=`
diff --git a/mlir/lib/Parser/Parser.cpp b/mlir/lib/Parser/Parser.cpp
--- a/mlir/lib/Parser/Parser.cpp
+++ b/mlir/lib/Parser/Parser.cpp
@@ -3573,7 +3573,8 @@
 ///  operation         ::= op-result-list?
 ///                        (generic-operation | custom-operation)
 ///                        trailing-location?
-///  generic-operation ::= string-literal '(' ssa-use-list? ')' attribute-dict?
+///  generic-operation ::= string-literal `(` ssa-use-list? `)`
+///                        (`(` region-list `)`)? attribute-dict?
 ///                        `:` function-type
 ///  custom-operation  ::= bare-id custom-operation-format
 ///  op-result-list    ::= op-result (`,` op-result)* `=`