diff --git a/src/Convert/Traverse.hs b/src/Convert/Traverse.hs
index 5e24145..5931cbe 100644
--- a/src/Convert/Traverse.hs
+++ b/src/Convert/Traverse.hs
@@ -452,10 +452,12 @@ traverseNestedGenItemsM :: Monad m => MapperM m GenItem -> MapperM m GenItem
 traverseNestedGenItemsM mapper = fullMapper
     where
         fullMapper genItem = gim genItem >>= mapper
-        gim (GenBlock x subItems) =
-            mapM fullMapper subItems >>= return . GenBlock x
-        gim (GenFor a b c d subItems) =
-            mapM fullMapper subItems >>= return . GenFor a b c d
+        gim (GenBlock x subItems) = do
+            subItems' <- mapM fullMapper subItems
+            return $ GenBlock x (concatMap flattenBlocks subItems')
+        gim (GenFor a b c d subItems) = do
+            subItems' <- mapM fullMapper subItems
+            return $ GenFor a b c d (concatMap flattenBlocks subItems')
         gim (GenIf e i1 i2) = do
             i1' <- fullMapper i1
             i2' <- fullMapper i2
@@ -468,6 +470,9 @@ traverseNestedGenItemsM mapper = fullMapper
         gim (GenModuleItem moduleItem) =
             return $ GenModuleItem moduleItem
         gim (GenNull) = return GenNull
+        flattenBlocks :: GenItem -> [GenItem]
+        flattenBlocks (GenBlock Nothing items) = items
+        flattenBlocks other = [other]
 
 traverseAsgnsM :: Monad m => MapperM m (LHS, Expr) -> MapperM m ModuleItem
 traverseAsgnsM mapper = moduleItemMapper
diff --git a/src/Language/SystemVerilog/Parser/Parse.y b/src/Language/SystemVerilog/Parser/Parse.y
index d214a7e..6873258 100644
--- a/src/Language/SystemVerilog/Parser/Parse.y
+++ b/src/Language/SystemVerilog/Parser/Parse.y
@@ -425,8 +425,7 @@ Stmt :: { Stmt }
   | Identifier      ";" { Subroutine $1 [] }
 StmtNonAsgn :: { Stmt }
   : ";" { Null }
-  | "begin"                DeclsAndStmts "end" opt(Tag) { Block Nothing   (fst $2) (snd $2) }
-  | "begin" ":" Identifier DeclsAndStmts "end" opt(Tag) { Block (Just $3) (fst $4) (snd $4) }
+  | "begin" opt(Tag) DeclsAndStmts "end" opt(Tag) { Block (combineTags $2 $5) (fst $3) (snd $3) }
   | "if" "(" Expr ")" Stmt "else" Stmt         { If $3 $5 $7        }
   | "if" "(" Expr ")" Stmt %prec NoElse        { If $3 $5 Null      }
   | "for" "(" Identifier "=" Expr ";" Expr ";" Identifier "=" Expr ")" Stmt { For ($3, $5) $7 ($9, $11) $13 }
@@ -588,8 +587,7 @@ GenItem :: { GenItem }
   | ModuleItem { genItemsToGenItem $ map GenModuleItem $1 }
 
 GenBlock :: { (Maybe Identifier, [GenItem]) }
-  : "begin"                GenItems "end" opt(Tag) { (Nothing, $2) }
-  | "begin" ":" Identifier GenItems "end" opt(Tag) { (Just $3, $4) }
+  : "begin" opt(Tag) GenItems "end" opt(Tag) { (combineTags $2 $5, $3) }
 
 GenCases :: { [GenCase] }
   : {- empty -}      { [] }
@@ -649,4 +647,12 @@ defaultFuncInput (Variable Input (Implicit rs) x a me) =
   Variable Input (Logic rs) x a me
 defaultFuncInput other = other
 
+combineTags :: Maybe Identifier -> Maybe Identifier -> Maybe Identifier
+combineTags (Just a) (Just b) =
+  if a == b
+    then Just a
+    else error $ "tag mismatch: " ++ show (a, b)
+combineTags Nothing other = other
+combineTags other   _     = other
+
 }