diff --git a/vlib/term/ui/termios_nix.c.v b/vlib/term/ui/termios_nix.c.v
index 8356b19b2be15d..a4b30b6bd0e018 100644
--- a/vlib/term/ui/termios_nix.c.v
+++ b/vlib/term/ui/termios_nix.c.v
@@ -258,12 +258,12 @@ fn (mut ctx Context) parse_events() {
 		mut event := &Event(unsafe { nil })
 		if ctx.read_buf[0] == 0x1b {
 			e, len := escape_sequence(ctx.read_buf.bytestr())
-			event = e
+			event = unsafe { e }
 			ctx.shift(len)
 		} else {
 			if ctx.read_all_bytes {
 				e, len := multi_char(ctx.read_buf.bytestr())
-				event = e
+				event = unsafe { e }
 				ctx.shift(len)
 			} else {
 				event = single_char(ctx.read_buf.bytestr())
diff --git a/vlib/toml/parser/parser.v b/vlib/toml/parser/parser.v
index 5446afd5bc71a5..88b69e94b4f51f 100644
--- a/vlib/toml/parser/parser.v
+++ b/vlib/toml/parser/parser.v
@@ -344,7 +344,7 @@ pub fn (mut p Parser) find_sub_table(key DottedKey) !&map[string]ast.Value {
 	ky << p.root_map_key
 	ky << key
 	if p.root_map_key.len == 0 {
-		ky = key
+		ky = unsafe { key }
 	}
 	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'locating "${ky}" in map ${ptr_str(p.root_map)}')
 	mut t := unsafe { &p.root_map }
@@ -1047,7 +1047,7 @@ pub fn (mut p Parser) double_array_of_tables_contents(target_key DottedKey) ![]a
 					// Parse `[d.e.f]`
 					p.ignore_while(space_formatting)
 					dotted_key := p.dotted_key()!
-					implicit_allocation_key = dotted_key
+					implicit_allocation_key = unsafe { dotted_key }
 					if dotted_key.len > 2 {
 						implicit_allocation_key = dotted_key[2..]
 					}
diff --git a/vlib/v/checker/assign.v b/vlib/v/checker/assign.v
index c5c9d97b4500e6..65fe4fc0210f0b 100644
--- a/vlib/v/checker/assign.v
+++ b/vlib/v/checker/assign.v
@@ -235,33 +235,6 @@ fn (mut c Checker) assign_stmt(mut node ast.AssignStmt) {
 					}
 				}
 			}
-			if left is ast.Ident && left.is_mut() && !c.inside_unsafe {
-				if left_type.is_ptr() && mut right is ast.Ident && !right.is_mut()
-					&& right_type.is_ptr() {
-					c.error('`${right.name}` is immutable, cannot have a mutable reference to an immutable object',
-						right.pos)
-				} else if mut right is ast.StructInit {
-					typ_sym := c.table.sym(right.typ)
-					for init_field in right.init_fields {
-						if field_info := c.table.find_field_with_embeds(typ_sym, init_field.name) {
-							if field_info.is_mut {
-								if init_field.expr is ast.Ident && !init_field.expr.is_mut()
-									&& init_field.typ.is_ptr() {
-									c.note('`${init_field.expr.name}` is immutable, cannot have a mutable reference to an immutable object',
-										init_field.pos)
-								} else if init_field.expr is ast.PrefixExpr {
-									if init_field.expr.op == .amp
-										&& init_field.expr.right is ast.Ident
-										&& !init_field.expr.right.is_mut() {
-										c.note('`${init_field.expr.right.name}` is immutable, cannot have a mutable reference to an immutable object',
-											init_field.expr.right.pos)
-									}
-								}
-							}
-						}
-					}
-				}
-			}
 		} else {
 			// Make sure the variable is mutable
 			c.fail_if_immutable(mut left)
@@ -275,6 +248,11 @@ fn (mut c Checker) assign_stmt(mut node ast.AssignStmt) {
 			// 	c.error('cannot assign a `none` value to a non-option variable', right.pos())
 			// }
 		}
+		if !c.inside_unsafe && !is_blank_ident && node.op in [.decl_assign, .assign]
+			&& left is ast.Ident && left.is_mut() {
+			// check if right-side is a immutable reference
+			c.fail_if_immutable_to_mutable(left_type, right_type, right)
+		}
 		if mut left is ast.Ident && left.info is ast.IdentVar && right is ast.Ident
 			&& right.name in c.global_names {
 			ident_var_info := left.info as ast.IdentVar
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 9fcadefba49685..9a7f4a1178373e 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -803,6 +803,78 @@ fn (mut c Checker) expand_iface_embeds(idecl &ast.InterfaceDecl, level int, ifac
 	return ares
 }
 
+// fail_if_immutable_to_mutable checks if there is a immutable reference on right-side of assignment for mutable var
+fn (mut c Checker) fail_if_immutable_to_mutable(left_type ast.Type, right_type ast.Type, right ast.Expr) bool {
+	match right {
+		ast.Ident {
+			if c.inside_unsafe || c.pref.translated || c.file.is_translated {
+				return true
+			}
+			if right.obj is ast.Var {
+				if left_type.is_ptr() && !right.is_mut() && right_type.is_ptr() {
+					c.error('`${right.name}` is immutable, cannot have a mutable reference to an immutable object',
+						right.pos)
+					return false
+				}
+				if !right.obj.is_mut
+					&& c.table.final_sym(right_type).kind in [.array, .array_fixed, .map] {
+					c.error('left-side of assignment expects a mutable reference, but variable `${right.name}` is immutable, declare it with `mut` to make it mutable or clone it',
+						right.pos)
+					return false
+				}
+			}
+		}
+		ast.IfExpr {
+			if c.inside_unsafe || c.pref.translated || c.file.is_translated {
+				return true
+			}
+			for branch in right.branches {
+				stmts := branch.stmts.filter(it is ast.ExprStmt)
+				if stmts.len > 0 {
+					last_expr := stmts.last() as ast.ExprStmt
+					c.fail_if_immutable_to_mutable(left_type, right_type, last_expr.expr)
+				}
+			}
+		}
+		ast.MatchExpr {
+			if c.inside_unsafe || c.pref.translated || c.file.is_translated {
+				return true
+			}
+			for branch in right.branches {
+				stmts := branch.stmts.filter(it is ast.ExprStmt)
+				if stmts.len > 0 {
+					last_expr := stmts.last() as ast.ExprStmt
+					c.fail_if_immutable_to_mutable(left_type, right_type, last_expr.expr)
+				}
+			}
+		}
+		ast.StructInit {
+			typ_sym := c.table.sym(right.typ)
+			for init_field in right.init_fields {
+				if field_info := c.table.find_field_with_embeds(typ_sym, init_field.name) {
+					if field_info.is_mut {
+						if init_field.expr is ast.Ident && !init_field.expr.is_mut()
+							&& init_field.typ.is_ptr() {
+							c.note('`${init_field.expr.name}` is immutable, cannot have a mutable reference to an immutable object',
+								init_field.pos)
+						} else if init_field.expr is ast.PrefixExpr {
+							if init_field.expr.op == .amp && init_field.expr.right is ast.Ident
+								&& !init_field.expr.right.is_mut() {
+								c.note('`${init_field.expr.right.name}` is immutable, cannot have a mutable reference to an immutable object',
+									init_field.expr.right.pos)
+							}
+						}
+					}
+				}
+			}
+		}
+		else {
+			return true
+		}
+	}
+	return true
+}
+
 // returns name and position of variable that needs write lock
 // also sets `is_changed` to true (TODO update the name to reflect this?)
 fn (mut c Checker) fail_if_immutable(mut expr ast.Expr) (string, token.Pos) {
@@ -4759,7 +4831,7 @@ fn (mut c Checker) index_expr(mut node ast.IndexExpr) ast.Type {
 			unwrapped_sym := c.table.final_sym(unwrapped_typ)
 			if unwrapped_sym.kind in [.map, .array, .array_fixed] {
 				typ = unwrapped_typ
-				typ_sym = unwrapped_sym
+				typ_sym = unsafe { unwrapped_sym }
 			}
 		}
 		else {}
diff --git a/vlib/v/checker/infix.v b/vlib/v/checker/infix.v
index 8370984c8ed1bd..732bd94e36e90b 100644
--- a/vlib/v/checker/infix.v
+++ b/vlib/v/checker/infix.v
@@ -314,12 +314,12 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 			if mut right_sym.info is ast.Alias && (right_sym.info.language != .c
 				&& c.mod == c.table.type_to_str(unwrapped_right_type).split('.')[0]
 				&& (right_final_sym.is_primitive() || right_final_sym.kind == .enum)) {
-				right_sym = right_final_sym
+				right_sym = unsafe { right_final_sym }
 			}
 			if mut left_sym.info is ast.Alias && (left_sym.info.language != .c
 				&& c.mod == c.table.type_to_str(unwrapped_left_type).split('.')[0]
 				&& (left_final_sym.is_primitive() || left_final_sym.kind == .enum)) {
-				left_sym = left_final_sym
+				left_sym = unsafe { left_final_sym }
 			}
 
 			if c.pref.translated && node.op in [.plus, .minus, .mul]
diff --git a/vlib/v/checker/tests/array_or_map_assign_err.out b/vlib/v/checker/tests/array_or_map_assign_err.out
index 88edda1e5ef09b..8e78ce29aca97d 100644
--- a/vlib/v/checker/tests/array_or_map_assign_err.out
+++ b/vlib/v/checker/tests/array_or_map_assign_err.out
@@ -1,3 +1,10 @@
+vlib/v/checker/tests/array_or_map_assign_err.vv:5:7: error: left-side of assignment expects a mutable reference, but variable `a1` is immutable, declare it with `mut` to make it mutable or clone it
+    3 |     a2 := a1
+    4 |     mut a3 := []int{}
+    5 |     a3 = a1
+      |          ~~
+    6 | 
+    7 |     m1 := {
 vlib/v/checker/tests/array_or_map_assign_err.vv:5:5: error: use `array2 = array1.clone()` instead of `array2 = array1` (or use `unsafe`)
     3 |     a2 := a1
     4 |     mut a3 := []int{}
@@ -12,6 +19,13 @@ vlib/v/checker/tests/array_or_map_assign_err.vv:10:8: error: cannot copy map: ca
       |           ~~
    11 |     mut m3 := map[string]int{}
    12 |     m3 = m1
+vlib/v/checker/tests/array_or_map_assign_err.vv:12:7: error: left-side of assignment expects a mutable reference, but variable `m1` is immutable, declare it with `mut` to make it mutable or clone it
+   10 |     m2 := m1
+   11 |     mut m3 := map[string]int{}
+   12 |     m3 = m1
+      |          ~~
+   13 | 
+   14 |     _ = a2
 vlib/v/checker/tests/array_or_map_assign_err.vv:12:7: error: cannot copy map: call `move` or `clone` method (or use a reference)
    10 |     m2 := m1
    11 |     mut m3 := map[string]int{}
diff --git a/vlib/v/checker/tests/fixed_array_conv.out b/vlib/v/checker/tests/fixed_array_conv.out
index bf6a171fe0d1c1..bdac3b30cad85f 100644
--- a/vlib/v/checker/tests/fixed_array_conv.out
+++ b/vlib/v/checker/tests/fixed_array_conv.out
@@ -5,6 +5,13 @@ vlib/v/checker/tests/fixed_array_conv.vv:6:5: warning: cannot cast a fixed array
       |     ~~~~~~~~~
     7 | _ = p
     8 | _ = ip
+vlib/v/checker/tests/fixed_array_conv.vv:3:5: error: left-side of assignment expects a mutable reference, but variable `arr` is immutable, declare it with `mut` to make it mutable or clone it
+    1 | arr := [2, 3]!
+    2 | mut p := unsafe { nil }
+    3 | p = arr
+      |     ~~~
+    4 | mut ip := &int(0)
+    5 | ip = arr
 vlib/v/checker/tests/fixed_array_conv.vv:3:3: error: mismatched types `voidptr` and `[2]int`
     1 | arr := [2, 3]!
     2 | mut p := unsafe { nil }
@@ -19,6 +26,13 @@ vlib/v/checker/tests/fixed_array_conv.vv:3:5: error: cannot assign to `p`: expec
       |     ~~~
     4 | mut ip := &int(0)
     5 | ip = arr
+vlib/v/checker/tests/fixed_array_conv.vv:5:6: error: left-side of assignment expects a mutable reference, but variable `arr` is immutable, declare it with `mut` to make it mutable or clone it
+    3 | p = arr
+    4 | mut ip := &int(0)
+    5 | ip = arr
+      |      ~~~
+    6 | _ = &int(arr)
+    7 | _ = p
 vlib/v/checker/tests/fixed_array_conv.vv:5:4: error: mismatched types `&int` and `[2]int`
     3 | p = arr
     4 | mut ip := &int(0)
diff --git a/vlib/v/checker/tests/immutable_to_mutable_err.out b/vlib/v/checker/tests/immutable_to_mutable_err.out
new file mode 100644
index 00000000000000..34b73b9b6369ce
--- /dev/null
+++ b/vlib/v/checker/tests/immutable_to_mutable_err.out
@@ -0,0 +1,28 @@
+vlib/v/checker/tests/immutable_to_mutable_err.vv:10:27: error: left-side of assignment expects a mutable reference, but variable `arr` is immutable, declare it with `mut` to make it mutable or clone it
+    8 | fn main() {
+    9 |     arr := [1, 2, 3] // declared as immutable!
+   10 |     mut arr_mut := if true { arr } else { []int{} }
+      |                              ~~~
+   11 |     mut arr_mut2 := match true {
+   12 |         true { arr }
+vlib/v/checker/tests/immutable_to_mutable_err.vv:12:10: error: left-side of assignment expects a mutable reference, but variable `arr` is immutable, declare it with `mut` to make it mutable or clone it
+   10 |     mut arr_mut := if true { arr } else { []int{} }
+   11 |     mut arr_mut2 := match true {
+   12 |         true { arr }
+      |                ~~~
+   13 |         else { [0] }
+   14 |     }
+vlib/v/checker/tests/immutable_to_mutable_err.vv:22:15: error: use `mut array2 := array1.clone()` instead of `mut array2 := array1` (or use `unsafe`)
+   20 | 
+   21 |     a := Test{}
+   22 |     mut arr_mut3 := a.foo
+      |                  ~~
+   23 |     arr_mut3[0] = 999
+   24 |     assert a.foo == [1, 2, 3]
+vlib/v/checker/tests/immutable_to_mutable_err.vv:26:15: error: use `mut array2 := array1.clone()` instead of `mut array2 := array1` (or use `unsafe`)
+   24 |     assert a.foo == [1, 2, 3]
+   25 | 
+   26 |     mut arr_mut4 := a.bar
+      |                  ~~
+   27 |     arr_mut4[0] = 999
+   28 |     assert a.bar == [1, 2, 3]
diff --git a/vlib/v/checker/tests/immutable_to_mutable_err.vv b/vlib/v/checker/tests/immutable_to_mutable_err.vv
new file mode 100644
index 00000000000000..b5a86100d11f38
--- /dev/null
+++ b/vlib/v/checker/tests/immutable_to_mutable_err.vv
@@ -0,0 +1,31 @@
+struct Test {
+pub:
+	bar []int = [1, 2, 3]
+pub mut:
+	foo []int = [1, 2, 3]
+}
+
+fn main() {
+	arr := [1, 2, 3] // declared as immutable!
+	mut arr_mut := if true { arr } else { []int{} }
+	mut arr_mut2 := match true {
+		true { arr }
+		else { [0] }
+	}
+	arr_mut[0] = 999
+	arr_mut2[1] = 999
+	println(arr)
+	println(arr)
+	assert arr == [1, 2, 3]
+
+	a := Test{}
+	mut arr_mut3 := a.foo
+	arr_mut3[0] = 999
+	assert a.foo == [1, 2, 3]
+
+	mut arr_mut4 := a.bar
+	arr_mut4[0] = 999
+	assert a.bar == [1, 2, 3]
+
+	_ := a.bar
+}
diff --git a/vlib/v/checker/tests/unsafe_fixed_array_assign.out b/vlib/v/checker/tests/unsafe_fixed_array_assign.out
index 248da72311265d..68b9223d232bf3 100644
--- a/vlib/v/checker/tests/unsafe_fixed_array_assign.out
+++ b/vlib/v/checker/tests/unsafe_fixed_array_assign.out
@@ -1,3 +1,10 @@
+vlib/v/checker/tests/unsafe_fixed_array_assign.vv:10:10: error: left-side of assignment expects a mutable reference, but variable `a` is immutable, declare it with `mut` to make it mutable or clone it
+    8 | }
+    9 | a := [&box]!
+   10 | mut b := a
+      |          ^
+   11 | b[0].num = 0
+   12 | println(a)
 vlib/v/checker/tests/unsafe_fixed_array_assign.vv:10:7: error: assignment from one fixed array to another with a pointer element type is prohibited outside of `unsafe`
     8 | }
     9 | a := [&box]!
diff --git a/vlib/v/gen/c/str.v b/vlib/v/gen/c/str.v
index 13a493e8bc80f6..24ded22e50e1b6 100644
--- a/vlib/v/gen/c/str.v
+++ b/vlib/v/gen/c/str.v
@@ -72,7 +72,7 @@ fn (mut g Gen) gen_expr_to_string(expr ast.Expr, etype ast.Type) {
 		parent_sym := g.table.sym(sym.info.parent_type)
 		if parent_sym.has_method('str') {
 			typ = sym.info.parent_type
-			sym = parent_sym
+			sym = unsafe { parent_sym }
 		}
 	}
 	sym_has_str_method, str_method_expects_ptr, _ := sym.str_method_info()
diff --git a/vlib/v/gen/js/str.v b/vlib/v/gen/js/str.v
index e685afd16d9453..2421f3120e5a44 100644
--- a/vlib/v/gen/js/str.v
+++ b/vlib/v/gen/js/str.v
@@ -87,7 +87,7 @@ fn (mut g JsGen) gen_expr_to_string(expr ast.Expr, etype ast.Type) {
 		parent_sym := g.table.sym(sym.info.parent_type)
 		if parent_sym.has_method('str') {
 			typ = sym.info.parent_type
-			sym = parent_sym
+			sym = unsafe { parent_sym }
 		}
 	}
 	sym_has_str_method, str_method_expects_ptr, _ := sym.str_method_info()
diff --git a/vlib/v/tests/generics/generic_selector_test.v b/vlib/v/tests/generics/generic_selector_test.v
index 4ba0226f22b89a..d57f316cbec83e 100644
--- a/vlib/v/tests/generics/generic_selector_test.v
+++ b/vlib/v/tests/generics/generic_selector_test.v
@@ -28,7 +28,7 @@ pub fn (mut l List[T]) append(mut node Node[T]) ?int {
 	for {
 		if curr_node != none {
 			if next_node := curr_node?.next {
-				curr_node = next_node
+				curr_node = unsafe { next_node }
 			} else {
 				curr_node?.next = &node
 				l.size = l.size + 1
diff --git a/vlib/v/token/keywords_matcher_trie.v b/vlib/v/token/keywords_matcher_trie.v
index 46dd9f6e51fb6e..2f0ed5953e69a1 100644
--- a/vlib/v/token/keywords_matcher_trie.v
+++ b/vlib/v/token/keywords_matcher_trie.v
@@ -160,7 +160,7 @@ pub fn (root &TrieNode) find(word string) int {
 		if child == unsafe { nil } {
 			return -1
 		}
-		node = child
+		node = unsafe { child }
 		idx++
 	}
 	return -1