diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 137ba91f23a..08351cf9f58 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -8774,6 +8774,7 @@ namespace ts {
             sig.minArgumentCount = minArgumentCount;
             sig.target = undefined;
             sig.mapper = undefined;
+            sig.unionSignatures = undefined;
             return sig;
         }
 
@@ -8782,6 +8783,7 @@ namespace ts {
                 /*resolvedTypePredicate*/ undefined, sig.minArgumentCount, sig.flags & SignatureFlags.PropagatingFlags);
             result.target = sig.target;
             result.mapper = sig.mapper;
+            result.unionSignatures = sig.unionSignatures;
             return result;
         }
 
diff --git a/tests/baselines/reference/typeParameterLeak.js b/tests/baselines/reference/typeParameterLeak.js
new file mode 100644
index 00000000000..37cd223e6ae
--- /dev/null
+++ b/tests/baselines/reference/typeParameterLeak.js
@@ -0,0 +1,29 @@
+//// [typeParameterLeak.ts]
+// Repro from #35655
+
+interface Box<T> { data: T }
+type BoxTypes = Box<{ x: string }> | Box<{ y: string }>;
+
+type BoxFactoryFactory<TBox> = TBox extends Box<infer T> ? {
+  (arg: T): BoxFactory<TBox> | undefined
+} : never;
+
+interface BoxFactory<A> {
+  getBox(): A,
+}
+
+declare const f: BoxFactoryFactory<BoxTypes>;
+const b = f({ x: "", y: "" })?.getBox();
+if (b) {
+  const x = b.data;
+}
+
+
+//// [typeParameterLeak.js]
+"use strict";
+// Repro from #35655
+var _a;
+var b = (_a = f({ x: "", y: "" })) === null || _a === void 0 ? void 0 : _a.getBox();
+if (b) {
+    var x = b.data;
+}
diff --git a/tests/baselines/reference/typeParameterLeak.symbols b/tests/baselines/reference/typeParameterLeak.symbols
new file mode 100644
index 00000000000..7eff175ae17
--- /dev/null
+++ b/tests/baselines/reference/typeParameterLeak.symbols
@@ -0,0 +1,63 @@
+=== tests/cases/compiler/typeParameterLeak.ts ===
+// Repro from #35655
+
+interface Box<T> { data: T }
+>Box : Symbol(Box, Decl(typeParameterLeak.ts, 0, 0))
+>T : Symbol(T, Decl(typeParameterLeak.ts, 2, 14))
+>data : Symbol(Box.data, Decl(typeParameterLeak.ts, 2, 18))
+>T : Symbol(T, Decl(typeParameterLeak.ts, 2, 14))
+
+type BoxTypes = Box<{ x: string }> | Box<{ y: string }>;
+>BoxTypes : Symbol(BoxTypes, Decl(typeParameterLeak.ts, 2, 28))
+>Box : Symbol(Box, Decl(typeParameterLeak.ts, 0, 0))
+>x : Symbol(x, Decl(typeParameterLeak.ts, 3, 21))
+>Box : Symbol(Box, Decl(typeParameterLeak.ts, 0, 0))
+>y : Symbol(y, Decl(typeParameterLeak.ts, 3, 42))
+
+type BoxFactoryFactory<TBox> = TBox extends Box<infer T> ? {
+>BoxFactoryFactory : Symbol(BoxFactoryFactory, Decl(typeParameterLeak.ts, 3, 56))
+>TBox : Symbol(TBox, Decl(typeParameterLeak.ts, 5, 23))
+>TBox : Symbol(TBox, Decl(typeParameterLeak.ts, 5, 23))
+>Box : Symbol(Box, Decl(typeParameterLeak.ts, 0, 0))
+>T : Symbol(T, Decl(typeParameterLeak.ts, 5, 53))
+
+  (arg: T): BoxFactory<TBox> | undefined
+>arg : Symbol(arg, Decl(typeParameterLeak.ts, 6, 3))
+>T : Symbol(T, Decl(typeParameterLeak.ts, 5, 53))
+>BoxFactory : Symbol(BoxFactory, Decl(typeParameterLeak.ts, 7, 10))
+>TBox : Symbol(TBox, Decl(typeParameterLeak.ts, 5, 23))
+
+} : never;
+
+interface BoxFactory<A> {
+>BoxFactory : Symbol(BoxFactory, Decl(typeParameterLeak.ts, 7, 10))
+>A : Symbol(A, Decl(typeParameterLeak.ts, 9, 21))
+
+  getBox(): A,
+>getBox : Symbol(BoxFactory.getBox, Decl(typeParameterLeak.ts, 9, 25))
+>A : Symbol(A, Decl(typeParameterLeak.ts, 9, 21))
+}
+
+declare const f: BoxFactoryFactory<BoxTypes>;
+>f : Symbol(f, Decl(typeParameterLeak.ts, 13, 13))
+>BoxFactoryFactory : Symbol(BoxFactoryFactory, Decl(typeParameterLeak.ts, 3, 56))
+>BoxTypes : Symbol(BoxTypes, Decl(typeParameterLeak.ts, 2, 28))
+
+const b = f({ x: "", y: "" })?.getBox();
+>b : Symbol(b, Decl(typeParameterLeak.ts, 14, 5))
+>f({ x: "", y: "" })?.getBox : Symbol(BoxFactory.getBox, Decl(typeParameterLeak.ts, 9, 25), Decl(typeParameterLeak.ts, 9, 25))
+>f : Symbol(f, Decl(typeParameterLeak.ts, 13, 13))
+>x : Symbol(x, Decl(typeParameterLeak.ts, 14, 13))
+>y : Symbol(y, Decl(typeParameterLeak.ts, 14, 20))
+>getBox : Symbol(BoxFactory.getBox, Decl(typeParameterLeak.ts, 9, 25), Decl(typeParameterLeak.ts, 9, 25))
+
+if (b) {
+>b : Symbol(b, Decl(typeParameterLeak.ts, 14, 5))
+
+  const x = b.data;
+>x : Symbol(x, Decl(typeParameterLeak.ts, 16, 7))
+>b.data : Symbol(Box.data, Decl(typeParameterLeak.ts, 2, 18), Decl(typeParameterLeak.ts, 2, 18))
+>b : Symbol(b, Decl(typeParameterLeak.ts, 14, 5))
+>data : Symbol(Box.data, Decl(typeParameterLeak.ts, 2, 18), Decl(typeParameterLeak.ts, 2, 18))
+}
+
diff --git a/tests/baselines/reference/typeParameterLeak.types b/tests/baselines/reference/typeParameterLeak.types
new file mode 100644
index 00000000000..e7aa09a2098
--- /dev/null
+++ b/tests/baselines/reference/typeParameterLeak.types
@@ -0,0 +1,50 @@
+=== tests/cases/compiler/typeParameterLeak.ts ===
+// Repro from #35655
+
+interface Box<T> { data: T }
+>data : T
+
+type BoxTypes = Box<{ x: string }> | Box<{ y: string }>;
+>BoxTypes : BoxTypes
+>x : string
+>y : string
+
+type BoxFactoryFactory<TBox> = TBox extends Box<infer T> ? {
+>BoxFactoryFactory : BoxFactoryFactory<TBox>
+
+  (arg: T): BoxFactory<TBox> | undefined
+>arg : T
+
+} : never;
+
+interface BoxFactory<A> {
+  getBox(): A,
+>getBox : () => A
+}
+
+declare const f: BoxFactoryFactory<BoxTypes>;
+>f : ((arg: { x: string; }) => BoxFactory<Box<{ x: string; }>> | undefined) | ((arg: { y: string; }) => BoxFactory<Box<{ y: string; }>> | undefined)
+
+const b = f({ x: "", y: "" })?.getBox();
+>b : Box<{ x: string; }> | Box<{ y: string; }> | undefined
+>f({ x: "", y: "" })?.getBox() : Box<{ x: string; }> | Box<{ y: string; }> | undefined
+>f({ x: "", y: "" })?.getBox : (() => Box<{ x: string; }>) | (() => Box<{ y: string; }>) | undefined
+>f({ x: "", y: "" }) : BoxFactory<Box<{ x: string; }>> | BoxFactory<Box<{ y: string; }>> | undefined
+>f : ((arg: { x: string; }) => BoxFactory<Box<{ x: string; }>> | undefined) | ((arg: { y: string; }) => BoxFactory<Box<{ y: string; }>> | undefined)
+>{ x: "", y: "" } : { x: string; y: string; }
+>x : string
+>"" : ""
+>y : string
+>"" : ""
+>getBox : (() => Box<{ x: string; }>) | (() => Box<{ y: string; }>) | undefined
+
+if (b) {
+>b : Box<{ x: string; }> | Box<{ y: string; }> | undefined
+
+  const x = b.data;
+>x : { x: string; } | { y: string; }
+>b.data : { x: string; } | { y: string; }
+>b : BoxTypes
+>data : { x: string; } | { y: string; }
+}
+
diff --git a/tests/cases/compiler/typeParameterLeak.ts b/tests/cases/compiler/typeParameterLeak.ts
new file mode 100644
index 00000000000..2827a4f5ab6
--- /dev/null
+++ b/tests/cases/compiler/typeParameterLeak.ts
@@ -0,0 +1,20 @@
+// @strict: true
+
+// Repro from #35655
+
+interface Box<T> { data: T }
+type BoxTypes = Box<{ x: string }> | Box<{ y: string }>;
+
+type BoxFactoryFactory<TBox> = TBox extends Box<infer T> ? {
+  (arg: T): BoxFactory<TBox> | undefined
+} : never;
+
+interface BoxFactory<A> {
+  getBox(): A,
+}
+
+declare const f: BoxFactoryFactory<BoxTypes>;
+const b = f({ x: "", y: "" })?.getBox();
+if (b) {
+  const x = b.data;
+}