diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 25cabe6bfe..c7bcdaca96 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -2218,28 +2218,27 @@ pub fn (mut c Checker) assign_stmt(mut assign_stmt ast.AssignStmt) {
 		// Single side check
 		match assign_stmt.op {
 			.assign {} // No need to do single side check for =. But here put it first for speed.
-			.plus_assign {
-				if !left_sym.is_number() && left_type != table.string_type && !left_sym.is_pointer() {
-					c.error('operator += not defined on left operand type `$left_sym.name`',
-						left.position())
-				} else if !right_sym.is_number() && right_type != table.string_type && !right_sym.is_pointer() {
-					c.error('operator += not defined on right operand type `$right_sym.name`',
-						right.position())
-				}
-				if right is ast.IntegerLiteral && right.str().int() == 1 {
-					c.error('use `++` instead of `+= 1`', assign_stmt.pos)
-				}
-			}
-			.minus_assign {
-				if !left_sym.is_number() && !left_sym.is_pointer() {
-					c.error('operator -= not defined on left operand type `$left_sym.name`',
+			.plus_assign, .minus_assign {
+				if left_type == table.string_type {
+					if assign_stmt.op != .plus_assign {
+						c.error('operator `$assign_stmt.op` not defined on left operand type `$left_sym.name`',
+							left.position())
+					}
+					if right_type != table.string_type {
+						c.error('invalid right operand: $left_sym.name $assign_stmt.op $right_sym.name',
+							right.position())
+					}
+				} else if !left_sym.is_number() && !left_sym.is_pointer() {
+					c.error('operator `$assign_stmt.op` not defined on left operand type `$left_sym.name`',
 						left.position())
 				} else if !right_sym.is_number() && !right_sym.is_pointer() {
-					c.error('operator -= not defined on right operand type `$right_sym.name`',
+					c.error('invalid right operand: $left_sym.name $assign_stmt.op $right_sym.name',
 						right.position())
-				}
-				if right is ast.IntegerLiteral && right.str().int() == 1 {
-					c.error('use `--` instead of `-= 1`', assign_stmt.pos)
+				} else if right is ast.IntegerLiteral {
+					if right.val == '1' {
+						op := if assign_stmt.op == .plus_assign { token.Kind.inc } else { token.Kind.dec }
+						c.error('use `$op` instead of `$assign_stmt.op 1`', assign_stmt.pos)
+					}
 				}
 			}
 			.mult_assign, .div_assign {
diff --git a/vlib/v/checker/tests/assign_expr_type_err_e.out b/vlib/v/checker/tests/assign_expr_type_err_e.out
index 943b11dafc..713316f762 100644
--- a/vlib/v/checker/tests/assign_expr_type_err_e.out
+++ b/vlib/v/checker/tests/assign_expr_type_err_e.out
@@ -1,4 +1,4 @@
-vlib/v/checker/tests/assign_expr_type_err_e.vv:3:2: error: operator -= not defined on left operand type `string`
+vlib/v/checker/tests/assign_expr_type_err_e.vv:3:2: error: operator `-=` not defined on left operand type `string`
     1 | fn main() {
     2 |     mut foo := 'hello'
     3 |     foo -= `a`
diff --git a/vlib/v/checker/tests/assign_expr_type_err_f.out b/vlib/v/checker/tests/assign_expr_type_err_f.out
index ac9b460bbd..180a100060 100644
--- a/vlib/v/checker/tests/assign_expr_type_err_f.out
+++ b/vlib/v/checker/tests/assign_expr_type_err_f.out
@@ -1,4 +1,4 @@
-vlib/v/checker/tests/assign_expr_type_err_f.vv:3:9: error: operator -= not defined on right operand type `bool`
+vlib/v/checker/tests/assign_expr_type_err_f.vv:3:9: error: invalid right operand: int -= bool
     1 | fn main() {
     2 |     mut foo := 10
     3 |     foo -= false
diff --git a/vlib/v/checker/tests/assign_expr_type_err_g.out b/vlib/v/checker/tests/assign_expr_type_err_g.out
index 95d8212ca2..75d6205065 100644
--- a/vlib/v/checker/tests/assign_expr_type_err_g.out
+++ b/vlib/v/checker/tests/assign_expr_type_err_g.out
@@ -1,4 +1,4 @@
-vlib/v/checker/tests/assign_expr_type_err_g.vv:3:2: error: operator += not defined on left operand type `bool`
+vlib/v/checker/tests/assign_expr_type_err_g.vv:3:2: error: operator `+=` not defined on left operand type `bool`
     1 | fn main() {
     2 |     mut foo := true
     3 |     foo += false
diff --git a/vlib/v/checker/tests/assign_expr_type_err_h.out b/vlib/v/checker/tests/assign_expr_type_err_h.out
index 0ee452f1ac..873f33b5f1 100644
--- a/vlib/v/checker/tests/assign_expr_type_err_h.out
+++ b/vlib/v/checker/tests/assign_expr_type_err_h.out
@@ -1,4 +1,4 @@
-vlib/v/checker/tests/assign_expr_type_err_h.vv:3:9: error: operator += not defined on right operand type `bool`
+vlib/v/checker/tests/assign_expr_type_err_h.vv:3:9: error: invalid right operand: string += bool
     1 | fn main() {
     2 |     mut foo := 'hello'
     3 |     foo += false
diff --git a/vlib/v/checker/tests/assign_expr_type_err_i.out b/vlib/v/checker/tests/assign_expr_type_err_i.out
index 1edbbc0719..3d14130464 100644
--- a/vlib/v/checker/tests/assign_expr_type_err_i.out
+++ b/vlib/v/checker/tests/assign_expr_type_err_i.out
@@ -1,4 +1,4 @@
-vlib/v/checker/tests/assign_expr_type_err_i.vv:3:9: error: cannot assign to `foo`: expected `f64`, not `string`
+vlib/v/checker/tests/assign_expr_type_err_i.vv:3:9: error: invalid right operand: f64 += string
     1 | fn main() {
     2 |     mut foo := 1.5
     3 |     foo += 'hello'