diff --git a/tests/baselines/reference/declarationEmitFBoundedTypeParams.js b/tests/baselines/reference/declarationEmitFBoundedTypeParams.js
new file mode 100644
index 00000000000..407dbf395e5
--- /dev/null
+++ b/tests/baselines/reference/declarationEmitFBoundedTypeParams.js
@@ -0,0 +1,20 @@
+//// [declarationEmitFBoundedTypeParams.ts]
+
+// Repro from #6040
+
+function append<a, b extends a>(result: a[], value: b): a[] {
+    result.push(value);
+    return result;
+}
+
+
+//// [declarationEmitFBoundedTypeParams.js]
+// Repro from #6040
+function append(result, value) {
+    result.push(value);
+    return result;
+}
+
+
+//// [declarationEmitFBoundedTypeParams.d.ts]
+declare function append<a, b extends a>(result: a[], value: b): a[];
diff --git a/tests/baselines/reference/declarationEmitFBoundedTypeParams.symbols b/tests/baselines/reference/declarationEmitFBoundedTypeParams.symbols
new file mode 100644
index 00000000000..bb12ea89600
--- /dev/null
+++ b/tests/baselines/reference/declarationEmitFBoundedTypeParams.symbols
@@ -0,0 +1,25 @@
+=== tests/cases/compiler/declarationEmitFBoundedTypeParams.ts ===
+
+// Repro from #6040
+
+function append<a, b extends a>(result: a[], value: b): a[] {
+>append : Symbol(append, Decl(declarationEmitFBoundedTypeParams.ts, 0, 0))
+>a : Symbol(a, Decl(declarationEmitFBoundedTypeParams.ts, 3, 16))
+>b : Symbol(b, Decl(declarationEmitFBoundedTypeParams.ts, 3, 18))
+>a : Symbol(a, Decl(declarationEmitFBoundedTypeParams.ts, 3, 16))
+>result : Symbol(result, Decl(declarationEmitFBoundedTypeParams.ts, 3, 32))
+>a : Symbol(a, Decl(declarationEmitFBoundedTypeParams.ts, 3, 16))
+>value : Symbol(value, Decl(declarationEmitFBoundedTypeParams.ts, 3, 44))
+>b : Symbol(b, Decl(declarationEmitFBoundedTypeParams.ts, 3, 18))
+>a : Symbol(a, Decl(declarationEmitFBoundedTypeParams.ts, 3, 16))
+
+    result.push(value);
+>result.push : Symbol(Array.push, Decl(lib.d.ts, --, --))
+>result : Symbol(result, Decl(declarationEmitFBoundedTypeParams.ts, 3, 32))
+>push : Symbol(Array.push, Decl(lib.d.ts, --, --))
+>value : Symbol(value, Decl(declarationEmitFBoundedTypeParams.ts, 3, 44))
+
+    return result;
+>result : Symbol(result, Decl(declarationEmitFBoundedTypeParams.ts, 3, 32))
+}
+
diff --git a/tests/baselines/reference/declarationEmitFBoundedTypeParams.types b/tests/baselines/reference/declarationEmitFBoundedTypeParams.types
new file mode 100644
index 00000000000..7f7198b3b6d
--- /dev/null
+++ b/tests/baselines/reference/declarationEmitFBoundedTypeParams.types
@@ -0,0 +1,26 @@
+=== tests/cases/compiler/declarationEmitFBoundedTypeParams.ts ===
+
+// Repro from #6040
+
+function append<a, b extends a>(result: a[], value: b): a[] {
+>append : <a, b extends a>(result: a[], value: b) => a[]
+>a : a
+>b : b
+>a : a
+>result : a[]
+>a : a
+>value : b
+>b : b
+>a : a
+
+    result.push(value);
+>result.push(value) : number
+>result.push : (...items: a[]) => number
+>result : a[]
+>push : (...items: a[]) => number
+>value : b
+
+    return result;
+>result : a[]
+}
+
diff --git a/tests/baselines/reference/typeInferenceFBoundedTypeParams.js b/tests/baselines/reference/typeInferenceFBoundedTypeParams.js
new file mode 100644
index 00000000000..3e30901df06
--- /dev/null
+++ b/tests/baselines/reference/typeInferenceFBoundedTypeParams.js
@@ -0,0 +1,39 @@
+//// [typeInferenceFBoundedTypeParams.ts]
+// Example from #6037
+
+function fold<a, r>(values: a[], result: r, fold: (result: r, value: a) => r): r {
+    for (let value of values) {
+        result = fold(result, value);
+    }
+    return result;
+}
+
+function append<a, b extends a>(values: a[], value: b): a[] {
+    values.push(value);
+    return values;
+}
+
+fold(
+    [1, 2, 3],
+    [] as [string, string][],
+    (result, value) => append(
+        result,
+        ["", ""]
+    )
+);
+
+
+//// [typeInferenceFBoundedTypeParams.js]
+// Example from #6037
+function fold(values, result, fold) {
+    for (var _i = 0, values_1 = values; _i < values_1.length; _i++) {
+        var value = values_1[_i];
+        result = fold(result, value);
+    }
+    return result;
+}
+function append(values, value) {
+    values.push(value);
+    return values;
+}
+fold([1, 2, 3], [], function (result, value) { return append(result, ["", ""]); });
diff --git a/tests/baselines/reference/typeInferenceFBoundedTypeParams.symbols b/tests/baselines/reference/typeInferenceFBoundedTypeParams.symbols
new file mode 100644
index 00000000000..f49d7b7524e
--- /dev/null
+++ b/tests/baselines/reference/typeInferenceFBoundedTypeParams.symbols
@@ -0,0 +1,71 @@
+=== tests/cases/compiler/typeInferenceFBoundedTypeParams.ts ===
+// Example from #6037
+
+function fold<a, r>(values: a[], result: r, fold: (result: r, value: a) => r): r {
+>fold : Symbol(fold, Decl(typeInferenceFBoundedTypeParams.ts, 0, 0))
+>a : Symbol(a, Decl(typeInferenceFBoundedTypeParams.ts, 2, 14))
+>r : Symbol(r, Decl(typeInferenceFBoundedTypeParams.ts, 2, 16))
+>values : Symbol(values, Decl(typeInferenceFBoundedTypeParams.ts, 2, 20))
+>a : Symbol(a, Decl(typeInferenceFBoundedTypeParams.ts, 2, 14))
+>result : Symbol(result, Decl(typeInferenceFBoundedTypeParams.ts, 2, 32))
+>r : Symbol(r, Decl(typeInferenceFBoundedTypeParams.ts, 2, 16))
+>fold : Symbol(fold, Decl(typeInferenceFBoundedTypeParams.ts, 2, 43))
+>result : Symbol(result, Decl(typeInferenceFBoundedTypeParams.ts, 2, 51))
+>r : Symbol(r, Decl(typeInferenceFBoundedTypeParams.ts, 2, 16))
+>value : Symbol(value, Decl(typeInferenceFBoundedTypeParams.ts, 2, 61))
+>a : Symbol(a, Decl(typeInferenceFBoundedTypeParams.ts, 2, 14))
+>r : Symbol(r, Decl(typeInferenceFBoundedTypeParams.ts, 2, 16))
+>r : Symbol(r, Decl(typeInferenceFBoundedTypeParams.ts, 2, 16))
+
+    for (let value of values) {
+>value : Symbol(value, Decl(typeInferenceFBoundedTypeParams.ts, 3, 12))
+>values : Symbol(values, Decl(typeInferenceFBoundedTypeParams.ts, 2, 20))
+
+        result = fold(result, value);
+>result : Symbol(result, Decl(typeInferenceFBoundedTypeParams.ts, 2, 32))
+>fold : Symbol(fold, Decl(typeInferenceFBoundedTypeParams.ts, 2, 43))
+>result : Symbol(result, Decl(typeInferenceFBoundedTypeParams.ts, 2, 32))
+>value : Symbol(value, Decl(typeInferenceFBoundedTypeParams.ts, 3, 12))
+    }
+    return result;
+>result : Symbol(result, Decl(typeInferenceFBoundedTypeParams.ts, 2, 32))
+}
+
+function append<a, b extends a>(values: a[], value: b): a[] {
+>append : Symbol(append, Decl(typeInferenceFBoundedTypeParams.ts, 7, 1))
+>a : Symbol(a, Decl(typeInferenceFBoundedTypeParams.ts, 9, 16))
+>b : Symbol(b, Decl(typeInferenceFBoundedTypeParams.ts, 9, 18))
+>a : Symbol(a, Decl(typeInferenceFBoundedTypeParams.ts, 9, 16))
+>values : Symbol(values, Decl(typeInferenceFBoundedTypeParams.ts, 9, 32))
+>a : Symbol(a, Decl(typeInferenceFBoundedTypeParams.ts, 9, 16))
+>value : Symbol(value, Decl(typeInferenceFBoundedTypeParams.ts, 9, 44))
+>b : Symbol(b, Decl(typeInferenceFBoundedTypeParams.ts, 9, 18))
+>a : Symbol(a, Decl(typeInferenceFBoundedTypeParams.ts, 9, 16))
+
+    values.push(value);
+>values.push : Symbol(Array.push, Decl(lib.d.ts, --, --))
+>values : Symbol(values, Decl(typeInferenceFBoundedTypeParams.ts, 9, 32))
+>push : Symbol(Array.push, Decl(lib.d.ts, --, --))
+>value : Symbol(value, Decl(typeInferenceFBoundedTypeParams.ts, 9, 44))
+
+    return values;
+>values : Symbol(values, Decl(typeInferenceFBoundedTypeParams.ts, 9, 32))
+}
+
+fold(
+>fold : Symbol(fold, Decl(typeInferenceFBoundedTypeParams.ts, 0, 0))
+
+    [1, 2, 3],
+    [] as [string, string][],
+    (result, value) => append(
+>result : Symbol(result, Decl(typeInferenceFBoundedTypeParams.ts, 17, 5))
+>value : Symbol(value, Decl(typeInferenceFBoundedTypeParams.ts, 17, 12))
+>append : Symbol(append, Decl(typeInferenceFBoundedTypeParams.ts, 7, 1))
+
+        result,
+>result : Symbol(result, Decl(typeInferenceFBoundedTypeParams.ts, 17, 5))
+
+        ["", ""]
+    )
+);
+
diff --git a/tests/baselines/reference/typeInferenceFBoundedTypeParams.types b/tests/baselines/reference/typeInferenceFBoundedTypeParams.types
new file mode 100644
index 00000000000..0ce04aabddf
--- /dev/null
+++ b/tests/baselines/reference/typeInferenceFBoundedTypeParams.types
@@ -0,0 +1,89 @@
+=== tests/cases/compiler/typeInferenceFBoundedTypeParams.ts ===
+// Example from #6037
+
+function fold<a, r>(values: a[], result: r, fold: (result: r, value: a) => r): r {
+>fold : <a, r>(values: a[], result: r, fold: (result: r, value: a) => r) => r
+>a : a
+>r : r
+>values : a[]
+>a : a
+>result : r
+>r : r
+>fold : (result: r, value: a) => r
+>result : r
+>r : r
+>value : a
+>a : a
+>r : r
+>r : r
+
+    for (let value of values) {
+>value : a
+>values : a[]
+
+        result = fold(result, value);
+>result = fold(result, value) : r
+>result : r
+>fold(result, value) : r
+>fold : (result: r, value: a) => r
+>result : r
+>value : a
+    }
+    return result;
+>result : r
+}
+
+function append<a, b extends a>(values: a[], value: b): a[] {
+>append : <a, b extends a>(values: a[], value: b) => a[]
+>a : a
+>b : b
+>a : a
+>values : a[]
+>a : a
+>value : b
+>b : b
+>a : a
+
+    values.push(value);
+>values.push(value) : number
+>values.push : (...items: a[]) => number
+>values : a[]
+>push : (...items: a[]) => number
+>value : b
+
+    return values;
+>values : a[]
+}
+
+fold(
+>fold(    [1, 2, 3],    [] as [string, string][],    (result, value) => append(        result,        ["", ""]    )) : [string, string][]
+>fold : <a, r>(values: a[], result: r, fold: (result: r, value: a) => r) => r
+
+    [1, 2, 3],
+>[1, 2, 3] : number[]
+>1 : number
+>2 : number
+>3 : number
+
+    [] as [string, string][],
+>[] as [string, string][] : [string, string][]
+>[] : undefined[]
+
+    (result, value) => append(
+>(result, value) => append(        result,        ["", ""]    ) : (result: [string, string][], value: number) => [string, string][]
+>result : [string, string][]
+>value : number
+>append(        result,        ["", ""]    ) : [string, string][]
+>append : <a, b extends a>(values: a[], value: b) => a[]
+
+        result,
+>result : [string, string][]
+
+        ["", ""]
+>["", ""] : [string, string]
+>"" : string
+>"" : string
+
+    )
+);
+
diff --git a/tests/cases/compiler/declarationEmitFBoundedTypeParams.ts b/tests/cases/compiler/declarationEmitFBoundedTypeParams.ts
new file mode 100644
index 00000000000..baa91ab7bb2
--- /dev/null
+++ b/tests/cases/compiler/declarationEmitFBoundedTypeParams.ts
@@ -0,0 +1,8 @@
+// @declaration: true
+
+// Repro from #6040
+
+function append<a, b extends a>(result: a[], value: b): a[] {
+    result.push(value);
+    return result;
+}
diff --git a/tests/cases/compiler/typeInferenceFBoundedTypeParams.ts b/tests/cases/compiler/typeInferenceFBoundedTypeParams.ts
new file mode 100644
index 00000000000..26f6be3fad2
--- /dev/null
+++ b/tests/cases/compiler/typeInferenceFBoundedTypeParams.ts
@@ -0,0 +1,22 @@
+// Example from #6037
+
+function fold<a, r>(values: a[], result: r, fold: (result: r, value: a) => r): r {
+    for (let value of values) {
+        result = fold(result, value);
+    }
+    return result;
+}
+
+function append<a, b extends a>(values: a[], value: b): a[] {
+    values.push(value);
+    return values;
+}
+
+fold(
+    [1, 2, 3],
+    [] as [string, string][],
+    (result, value) => append(
+        result,
+        ["", ""]
+    )
+);