diff --git a/cmd/tools/vdoc/highlight.v b/cmd/tools/vdoc/highlight.v
index b641b0cc28f746..ca0279627a8fba 100644
--- a/cmd/tools/vdoc/highlight.v
+++ b/cmd/tools/vdoc/highlight.v
@@ -83,7 +83,7 @@ fn color_highlight(code string, tb &ast.Table) string {
 						&& (next_tok.kind != .lpar || prev.kind !in [.key_fn, .rpar]) {
 						tok_typ = .builtin
 					} else if
-						(next_tok.kind in [.lcbr, .rpar, .eof, .comma, .pipe, .name, .rcbr, .assign, .key_pub, .key_mut, .pipe, .comma, .comment, .lt, .lsbr]
+						(next_tok.kind in [.lcbr, .rpar, .eof, .name, .rcbr, .assign, .key_pub, .key_mut, .pipe, .comma, .comment, .lt, .lsbr]
 						&& next_tok.lit !in highlight_builtin_types)
 						&& (prev.kind in [.name, .amp, .lcbr, .rsbr, .key_type, .assign, .dot, .not, .question, .rpar, .key_struct, .key_enum, .pipe, .key_interface, .comment, .ellipsis, .comma]
 						&& prev.lit !in highlight_builtin_types)
diff --git a/vlib/v/checker/infix.v b/vlib/v/checker/infix.v
index 3187823758f46b..06327571f4f21e 100644
--- a/vlib/v/checker/infix.v
+++ b/vlib/v/checker/infix.v
@@ -241,6 +241,9 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 							c.error('left operand to `${node.op}` does not match the array element type: ${err.msg()}',
 								left_right_pos)
 						}
+						if mut node.right is ast.ArrayInit {
+							c.check_duplicated_items(node.right)
+						}
 					} else {
 						if mut node.right is ast.ArrayInit {
 							for i, typ in node.right.expr_types {
@@ -953,6 +956,18 @@ fn (mut c Checker) check_div_mod_by_zero(expr ast.Expr, op_kind token.Kind) {
 	}
 }
 
+fn (mut c Checker) check_duplicated_items(node &ast.ArrayInit) {
+	mut unique_items := []string{cap: node.exprs.len}
+	for item in node.exprs {
+		item_str := item.str()
+		if item_str in unique_items {
+			c.note('item `${item_str}` is duplicated in the list', item.pos())
+		} else {
+			unique_items << item_str
+		}
+	}
+}
+
 fn (mut c Checker) check_like_operator(node &ast.InfixExpr) ast.Type {
 	if node.left !is ast.Ident || !node.left_type.is_string() {
 		c.error('the left operand of the `like` operator must be an identifier with a string type',
diff --git a/vlib/v/checker/str.v b/vlib/v/checker/str.v
index c196f2056f9351..142a4e42e6b617 100644
--- a/vlib/v/checker/str.v
+++ b/vlib/v/checker/str.v
@@ -96,8 +96,7 @@ fn (mut c Checker) string_inter_lit(mut node ast.StringInterLiteral) ast.Type {
 			}
 			if ((typ.is_unsigned() && fmt !in [`u`, `x`, `X`, `o`, `c`, `b`])
 				|| (typ.is_signed() && fmt !in [`d`, `x`, `X`, `o`, `c`, `b`])
-				|| (typ.is_int_literal()
-				&& fmt !in [`d`, `c`, `x`, `X`, `o`, `u`, `x`, `X`, `o`, `b`])
+				|| (typ.is_int_literal() && fmt !in [`d`, `c`, `x`, `X`, `o`, `u`, `b`])
 				|| (typ.is_float() && fmt !in [`E`, `F`, `G`, `e`, `f`, `g`])
 				|| (typ.is_pointer() && fmt !in [`p`, `x`, `X`])
 				|| (typ.is_string() && fmt !in [`s`, `S`, `r`, `R`])
diff --git a/vlib/v/checker/tests/infix_dup_in_err.out b/vlib/v/checker/tests/infix_dup_in_err.out
new file mode 100644
index 00000000000000..4feb328daf69c9
--- /dev/null
+++ b/vlib/v/checker/tests/infix_dup_in_err.out
@@ -0,0 +1,12 @@
+vlib/v/checker/tests/infix_dup_in_err.vv:1:16: notice: item `2` is duplicated in the list
+    1 | if 1 in [1, 2, 2, 2] { println('ok') }
+      |                ^
+    2 | 
+    3 | a := `a`
+vlib/v/checker/tests/infix_dup_in_err.vv:4:20: notice: item `a` is duplicated in the list
+    2 | 
+    3 | a := `a`
+    4 | if `a` in [`c`, a, a] { println('ok') }
+      |                    ^
+    5 | 
+    6 | println('done')
diff --git a/vlib/v/checker/tests/infix_dup_in_err.vv b/vlib/v/checker/tests/infix_dup_in_err.vv
new file mode 100644
index 00000000000000..06b9e37b9337d4
--- /dev/null
+++ b/vlib/v/checker/tests/infix_dup_in_err.vv
@@ -0,0 +1,6 @@
+if 1 in [1, 2, 2, 2] { println('ok') }
+
+a := `a`
+if `a` in [`c`, a, a] { println('ok') }
+
+println('done')
\ No newline at end of file