diff --git a/src/Convert/Simplify.hs b/src/Convert/Simplify.hs
index 569761f..f217e69 100644
--- a/src/Convert/Simplify.hs
+++ b/src/Convert/Simplify.hs
@@ -49,9 +49,12 @@ traverseExprM = traverseNestedExprsM $ stately convertExpr
 
 convertExpr :: Info -> Expr -> Expr
 convertExpr info (Cast (Right c) e) =
-    if sized == e
-        then Cast (Right c') e
-        else sized
+    case c' of
+        Number _ ->
+            if sized == e
+                then Cast (Right c') e
+                else sized
+        _ -> Cast (Right c') e
     where
         c' = simplify $ traverseNestedExprs (substitute info) (simplify c)
         sized = sizedExpr "" c' e
diff --git a/src/Convert/SizeCast.hs b/src/Convert/SizeCast.hs
index ae7cda3..7d6ab26 100644
--- a/src/Convert/SizeCast.hs
+++ b/src/Convert/SizeCast.hs
@@ -15,7 +15,7 @@ import Convert.Traverse
 import Language.SystemVerilog.AST
 
 type TypeMap = Map.Map Identifier Type
-type CastSet  = Set.Set (Int, Signing)
+type CastSet  = Set.Set (Expr, Signing)
 
 type ST = StateT TypeMap (Writer CastSet)
 
@@ -58,38 +58,42 @@ traverseExprM =
     traverseNestedExprsM convertExprM
     where
         convertExprM :: Expr -> ST Expr
-        convertExprM (Cast (Right (Number n)) e) = do
+        convertExprM (Cast (Right s) e) = do
             typeMap <- get
-            case (readNumber n, exprSigning typeMap e) of
-                (Just size, Just sg) -> do
-                    lift $ tell $ Set.singleton (size, sg)
-                    let f = castFnName size sg
+            case exprSigning typeMap e of
+                Just sg -> do
+                    lift $ tell $ Set.singleton (s, sg)
+                    let f = castFnName s sg
                     let args = Args [Just e] []
                     return $ Call Nothing f args
-                _ -> return $ Cast (Right $ Number n) e
+                _ -> return $ Cast (Right s) e
         convertExprM other = return other
 
 
-castFn :: Int -> Signing -> Description
-castFn n sg =
+castFn :: Expr -> Signing -> Description
+castFn e sg =
     PackageItem $
     Function (Just Automatic) t fnName [decl] [Return $ Ident inp]
     where
         inp = "inp"
-        r = (Number $ show (n - 1), Number "0")
+        r = (BinOp Sub e (Number "1"), Number "0")
         t = IntegerVector TLogic sg [r]
-        fnName = castFnName n sg
+        fnName = castFnName e sg
         decl = Variable Input t inp [] Nothing
 
-castFnName :: Int -> Signing -> String
-castFnName n sg =
-    if n <= 0
-        then error $ "cannot have non-positive size cast: " ++ show n
-        else
-            if sg == Unspecified
-                then init name
-                else name
-    where name = "sv2v_cast_" ++ show n ++ "_" ++ show sg
+castFnName :: Expr -> Signing -> String
+castFnName e sg =
+    if sg == Unspecified
+        then init name
+        else name
+    where
+        sizeStr = case e of
+            Number n ->
+                case readNumber n of
+                    Just v -> show v
+                    _ -> shortHash e
+            _ -> shortHash e
+        name = "sv2v_cast_" ++ sizeStr ++ "_" ++ show sg
 
 exprSigning :: TypeMap -> Expr -> Maybe Signing
 exprSigning typeMap (Ident x) =
diff --git a/test/basic/cast.sv b/test/basic/cast.sv
index 97b5c3f..99fe1e4 100644
--- a/test/basic/cast.sv
+++ b/test/basic/cast.sv
@@ -1,4 +1,5 @@
 module top;
+    parameter WIDTH = 32;
     initial begin
         logic [31:0] w = 1234;
         int x = -235;
@@ -16,6 +17,10 @@ module top;
         $display("%b %b", x, 40'(x));
         $display("%b %b", y, 40'(y));
         $display("%b %b", z, 40'(z));
+        $display("%0d %0d", w, ($clog2(WIDTH))'(w));
+        $display("%0d %0d", x, ($clog2(WIDTH))'(x));
+        $display("%0d %0d", y, ($clog2(WIDTH))'(y));
+        $display("%0d %0d", z, ($clog2(WIDTH))'(z));
     end
     localparam bit foo = '0;
     localparam logic [31:0] bar = 32'(foo);
diff --git a/test/basic/cast.v b/test/basic/cast.v
index 6834033..99fd8aa 100644
--- a/test/basic/cast.v
+++ b/test/basic/cast.v
@@ -20,6 +20,10 @@ module top;
         $display("%b %b", x, {8'hFF, x});
         $display("%b %b", y, {8'b0, y});
         $display("%b %b", z, {35'b0, z});
+        $display("%0d %0d", w, w[4:0]);
+        $display("%0d %0d", x, $signed(x[4:0]));
+        $display("%0d %0d", y, $signed(y[4:0]));
+        $display("%0d %0d", z, z[4:0]);
     end
     localparam [0:0] foo = 0;
     localparam [31:0] bar = 32'b0;