diff --git a/refurb/checks/common.py b/refurb/checks/common.py
index 5bcc097..8895cd5 100644
--- a/refurb/checks/common.py
+++ b/refurb/checks/common.py
@@ -329,6 +329,10 @@ def _stringify(node: Node) -> str:
         case TupleExpr(items=items):
             inner = ", ".join(stringify(x) for x in items)
 
+            if len(items) == 1:
+                # single element tuples need a trailing comma
+                inner += ","
+
             return f"({inner})"
 
         case CallExpr():
@@ -387,6 +391,11 @@ def _stringify(node: Node) -> str:
 
             return f"[{inner}]"
 
+        case SetExpr(items=items):
+            inner = ", ".join(stringify(x) for x in items)
+
+            return f"{{{inner}}}"
+
     raise ValueError
 
 
diff --git a/refurb/checks/iterable/no_single_item_in.py b/refurb/checks/iterable/no_single_item_in.py
index 591fd45..87470ca 100644
--- a/refurb/checks/iterable/no_single_item_in.py
+++ b/refurb/checks/iterable/no_single_item_in.py
@@ -1,7 +1,8 @@
 from dataclasses import dataclass
 
-from mypy.nodes import ComparisonExpr, ListExpr, TupleExpr
+from mypy.nodes import ComparisonExpr, ListExpr, SetExpr, TupleExpr
 
+from refurb.checks.common import stringify
 from refurb.error import Error
 
 
@@ -34,13 +35,12 @@ def check(node: ComparisonExpr, errors: list[Error]) -> None:
     match node:
         case ComparisonExpr(
             operators=["in" | "not in" as oper],
-            operands=[_, ListExpr() | TupleExpr() as expr],
+            operands=[lhs, ListExpr() | TupleExpr() | SetExpr() as expr],
         ) if len(expr.items) == 1:
             new_oper = "==" if oper == "in" else "!="
 
-            if isinstance(expr, ListExpr):
-                msg = f"Replace `x {oper} [y]` with `x {new_oper} y`"
-            else:
-                msg = f"Replace `x {oper} (y,)` with `x {new_oper} y`"
+            new = f"{stringify(lhs)} {new_oper} {stringify(expr.items[0])}"
+
+            msg = f"Replace `{stringify(node)}` with `{new}`"
 
             errors.append(ErrorInfo.from_node(node, msg))
diff --git a/test/data/err_171.py b/test/data/err_171.py
index fdc2b30..6cbc524 100644
--- a/test/data/err_171.py
+++ b/test/data/err_171.py
@@ -2,8 +2,10 @@
 
 _ = 1 in (1,)
 _ = 1 in [1]  # noqa: FURB109
+_ = 1 in {1}
 _ = 1 not in (1,)
 _ = 1 not in [1]  # noqa: FURB109
+_ = 1 not in {1}  # noqa: FURB109
 
 
 # these should not
diff --git a/test/data/err_171.txt b/test/data/err_171.txt
index c952f32..b0cfad7 100644
--- a/test/data/err_171.txt
+++ b/test/data/err_171.txt
@@ -1,4 +1,6 @@
-test/data/err_171.py:3:5 [FURB171]: Replace `x in (y,)` with `x == y`
-test/data/err_171.py:4:5 [FURB171]: Replace `x in [y]` with `x == y`
-test/data/err_171.py:5:5 [FURB171]: Replace `x not in (y,)` with `x != y`
-test/data/err_171.py:6:5 [FURB171]: Replace `x not in [y]` with `x != y`
+test/data/err_171.py:3:5 [FURB171]: Replace `1 in (1,)` with `1 == 1`
+test/data/err_171.py:4:5 [FURB171]: Replace `1 in [1]` with `1 == 1`
+test/data/err_171.py:5:5 [FURB171]: Replace `1 in {1}` with `1 == 1`
+test/data/err_171.py:6:5 [FURB171]: Replace `1 not in (1,)` with `1 != 1`
+test/data/err_171.py:7:5 [FURB171]: Replace `1 not in [1]` with `1 != 1`
+test/data/err_171.py:8:5 [FURB171]: Replace `1 not in {1}` with `1 != 1`