diff --git a/src/Convert/SizeCast.hs b/src/Convert/SizeCast.hs
index 2c46b98..e9ec593 100644
--- a/src/Convert/SizeCast.hs
+++ b/src/Convert/SizeCast.hs
@@ -66,8 +66,8 @@ traverseExprM =
                     where
                         str = (show size) ++ "'d"  ++ (show num)
                         size = s'
-                        num = if size == 32
-                            then n'
+                        num = if size >= 32
+                            then n' -- already read as 32 bits
                             else n' `mod` (2 ^ s')
                 _ -> convertCastM (Number s) (Number n)
         convertExprM (orig @ (Cast (Right DimsFn{}) _)) =
diff --git a/src/Language/SystemVerilog/AST/Expr.hs b/src/Language/SystemVerilog/AST/Expr.hs
index 2031f8a..52f1603 100644
--- a/src/Language/SystemVerilog/AST/Expr.hs
+++ b/src/Language/SystemVerilog/AST/Expr.hs
@@ -207,7 +207,13 @@ readNumber ('\'' : 'h' : rest) =
     case readHex rest of
         [(v, _)] -> Just v
         _ -> Nothing
-readNumber n = readMaybe n
+readNumber n =
+    case readMaybe n of
+        Nothing -> Nothing
+        Just res ->
+            if show res == n
+                then Just res
+                else Nothing
 
 showUniOpPrec :: Expr -> ShowS
 showUniOpPrec (e @ UniOp{}) = (showParen True . shows) e
diff --git a/test/basic/cast.sv b/test/basic/cast.sv
index 51d755e..abef50e 100644
--- a/test/basic/cast.sv
+++ b/test/basic/cast.sv
@@ -23,6 +23,12 @@ module top;
         $display("%0d %0d", y, ($clog2(WIDTH))'(y));
         $display("%0d %0d", z, ($clog2(WIDTH))'(z));
         $display("%b", 32'(4));
+        $display("%b", 33'(4));
+        $display("%b", 33'(64'hFFFF_FFFF_FFFF_FFFF));
+        $display("%b", 32'(4294967296));
+        $display("%b", 33'(4294967296));
+        $display("%b", 32'(4294967297));
+        $display("%b", 33'(4294967297));
     end
 
     localparam bit foo = '0;
diff --git a/test/basic/cast.v b/test/basic/cast.v
index 22ceaca..96c1cac 100644
--- a/test/basic/cast.v
+++ b/test/basic/cast.v
@@ -26,6 +26,12 @@ module top;
         $display("%0d %0d", y, $signed(y[4:0]));
         $display("%0d %0d", z, z[4:0]);
         $display("%b", 32'd4);
+        $display("%b", 33'd4);
+        $display("%b", 33'h1_FFFF_FFFF);
+        $display("%b", 32'd0);
+        $display("%b", 33'd4294967296);
+        $display("%b", 32'd1);
+        $display("%b", 33'd4294967297);
     end
 
     localparam [0:0] foo = 0;