diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 552b4a57bf..cdc8df6954 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -2922,8 +2922,7 @@ pub fn (mut c Checker) selector_expr(mut node ast.SelectorExpr) ast.Type {
 	if field_name.len > 0 && field_name[0].is_capital() && sym.info is ast.Struct
 		&& sym.language == .v {
 		// x.Foo.y => access the embedded struct
-		sym_info := sym.info as ast.Struct
-		for embed in sym_info.embeds {
+		for embed in sym.info.embeds {
 			embed_sym := c.table.get_type_symbol(embed)
 			if embed_sym.embed_name() == field_name {
 				node.typ = embed
@@ -4271,7 +4270,6 @@ fn (mut c Checker) for_stmt(mut node ast.ForStmt) {
 		if infix.op == .key_is {
 			if (infix.left is ast.Ident || infix.left is ast.SelectorExpr)
 				&& infix.right is ast.TypeNode {
-				right_expr := infix.right as ast.TypeNode
 				is_variable := if mut infix.left is ast.Ident {
 					infix.left.kind == .variable
 				} else {
@@ -4281,7 +4279,8 @@ fn (mut c Checker) for_stmt(mut node ast.ForStmt) {
 				left_sym := c.table.get_type_symbol(left_type)
 				if is_variable {
 					if left_sym.kind in [.sum_type, .interface_] {
-						c.smartcast(infix.left, infix.left_type, right_expr.typ, mut node.scope)
+						c.smartcast(infix.left, infix.left_type, infix.right.typ, mut
+							node.scope)
 					}
 				}
 			}
@@ -4667,12 +4666,12 @@ pub fn (mut c Checker) expr(node ast.Expr) ast.Type {
 				if !c.table.sumtype_has_variant(node.expr_type, node.typ) {
 					c.error('cannot cast `$expr_type_sym.name` to `$type_sym.name`', node.pos)
 				}
-			} else {
-				// mut s := 'cannot cast non-sum type `$expr_type_sym.name` using `as`'
-				// if type_sym.kind == .sum_type {
-				// 	s += ' - use e.g. `${type_sym.name}(some_expr)` instead.'
-				// }
-				// c.error(s, node.pos)
+			} else if node.expr_type != node.typ {
+				mut s := 'cannot cast non-sum type `$expr_type_sym.name` using `as`'
+				if type_sym.kind == .sum_type {
+					s += ' - use e.g. `${type_sym.name}(some_expr)` instead.'
+				}
+				c.error(s, node.pos)
 			}
 			return node.typ
 		}
@@ -5998,7 +5997,7 @@ pub fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 					} else if branch.cond.right is ast.TypeNode && left is ast.TypeNode
 						&& sym.kind == .interface_ {
 						// is interface
-						checked_type := c.unwrap_generic((left as ast.TypeNode).typ)
+						checked_type := c.unwrap_generic(left.typ)
 						should_skip = !c.table.type_implements_interface(checked_type,
 							got_type)
 					} else if left is ast.TypeNode {
@@ -6187,8 +6186,7 @@ fn (mut c Checker) comp_if_branch(cond ast.Expr, pos token.Position) bool {
 				.key_is, .not_is {
 					if cond.left is ast.TypeNode && cond.right is ast.TypeNode {
 						// `$if Foo is Interface {`
-						type_node := cond.right as ast.TypeNode
-						sym := c.table.get_type_symbol(type_node.typ)
+						sym := c.table.get_type_symbol(cond.right.typ)
 						if sym.kind != .interface_ {
 							c.expr(cond.left)
 							// c.error('`$sym.name` is not an interface', cond.right.position())
diff --git a/vlib/v/checker/tests/sum.out b/vlib/v/checker/tests/sum.out
new file mode 100644
index 0000000000..5c92692ca7
--- /dev/null
+++ b/vlib/v/checker/tests/sum.out
@@ -0,0 +1,28 @@
+vlib/v/checker/tests/sum.vv:5:8: error: cannot cast non-sum type `int` using `as`
+    3 | fn non_sum() {
+    4 |     v := 4
+    5 |     _ = v as rune
+      |           ~~
+    6 |     _ = v as Var
+    7 | }
+vlib/v/checker/tests/sum.vv:6:8: error: cannot cast non-sum type `int` using `as` - use e.g. `Var(some_expr)` instead.
+    4 |     v := 4
+    5 |     _ = v as rune
+    6 |     _ = v as Var
+      |           ~~
+    7 | }
+    8 |
+vlib/v/checker/tests/sum.vv:10:7: error: cannot cast `rune` to `Var`
+    8 | 
+    9 | fn sum() {
+   10 |     _ := Var(`J`)
+      |          ~~~~~~~~
+   11 |     mut s2 := Var('')
+   12 |     s2 = true
+vlib/v/checker/tests/sum.vv:12:7: error: cannot assign to `s2`: expected `Var`, not `bool`
+   10 |     _ := Var(`J`)
+   11 |     mut s2 := Var('')
+   12 |     s2 = true
+      |          ~~~~
+   13 |     _ = s2
+   14 | }
diff --git a/vlib/v/checker/tests/sum.vv b/vlib/v/checker/tests/sum.vv
new file mode 100644
index 0000000000..6796a2e58f
--- /dev/null
+++ b/vlib/v/checker/tests/sum.vv
@@ -0,0 +1,14 @@
+type Var = int | string
+
+fn non_sum() {
+	v := 4
+	_ = v as rune
+	_ = v as Var
+}
+
+fn sum() {
+	_ := Var(`J`)
+	mut s2 := Var('')
+	s2 = true
+	_ = s2
+}
diff --git a/vlib/v/gen/c/comptime.v b/vlib/v/gen/c/comptime.v
index 54462a4998..e6c29a1889 100644
--- a/vlib/v/gen/c/comptime.v
+++ b/vlib/v/gen/c/comptime.v
@@ -325,7 +325,7 @@ fn (mut g Gen) comp_if_cond(cond ast.Expr) bool {
 						interface_sym := g.table.get_type_symbol(got_type)
 						if interface_sym.info is ast.Interface {
 							// q := g.table.get_type_symbol(interface_sym.info.types[0])
-							checked_type := g.unwrap_generic((left as ast.TypeNode).typ)
+							checked_type := g.unwrap_generic(left.typ)
 							// TODO PERF this check is run twice (also in the checker)
 							// store the result in a field
 							is_true := g.table.type_implements_interface(checked_type,
diff --git a/vlib/v/gen/js/js.v b/vlib/v/gen/js/js.v
index fefe9da739..f9b83faced 100644
--- a/vlib/v/gen/js/js.v
+++ b/vlib/v/gen/js/js.v
@@ -850,8 +850,7 @@ fn (mut g JsGen) gen_enum_decl(it ast.EnumDecl) {
 	for field in it.fields {
 		g.write('$field.name: ')
 		if field.has_expr && field.expr is ast.IntegerLiteral {
-			e := field.expr as ast.IntegerLiteral
-			i = e.val.int()
+			i = field.expr.val.int()
 		}
 		g.writeln('$i,')
 		i++
diff --git a/vlib/v/gen/js/sourcemap/mappings.v b/vlib/v/gen/js/sourcemap/mappings.v
index 71ba0c031b..dfe1318798 100644
--- a/vlib/v/gen/js/sourcemap/mappings.v
+++ b/vlib/v/gen/js/sourcemap/mappings.v
@@ -150,8 +150,8 @@ fn compare_by_generated_positions_inflated(mapping_a Mapping, mapping_b Mapping)
 
 	if mapping_a.source_position.type_name() == mapping_b.source_position.type_name()
 		&& mapping_b.source_position is SourcePosition {
-		if
-			(mapping_a.source_position as SourcePosition).source_line != (mapping_b.source_position as SourcePosition).source_line || (mapping_a.source_position as SourcePosition).source_column != (mapping_b.source_position as SourcePosition).source_column {
+		if mapping_a.source_position.source_line != mapping_b.source_position.source_line
+			|| mapping_a.source_position.source_column != mapping_b.source_position.source_column {
 			return true
 		}
 	} else {
@@ -161,8 +161,8 @@ fn compare_by_generated_positions_inflated(mapping_a Mapping, mapping_b Mapping)
 	}
 
 	if mapping_a.names_ind.type_name() == mapping_b.names_ind.type_name()
-		&& mapping_a.names_ind is IndexNumber {
-		return (mapping_a.names_ind as IndexNumber) != (mapping_b.names_ind as IndexNumber)
+		&& mapping_a.names_ind is IndexNumber && mapping_b.names_ind is IndexNumber {
+		return mapping_a.names_ind != mapping_b.names_ind
 	} else {
 		return mapping_a.names_ind.type_name() != mapping_b.names_ind.type_name()
 	}
diff --git a/vlib/v/parser/sql.v b/vlib/v/parser/sql.v
index 6587614565..28a71570db 100644
--- a/vlib/v/parser/sql.v
+++ b/vlib/v/parser/sql.v
@@ -34,8 +34,7 @@ fn (mut p Parser) sql_expr() ast.Expr {
 		if !is_count && where_expr is ast.InfixExpr {
 			e := where_expr as ast.InfixExpr
 			if e.op == .eq && e.left is ast.Ident {
-				ident := e.left as ast.Ident
-				if ident.name == 'id' {
+				if e.left.name == 'id' {
 					query_one = true
 				}
 			}