diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 3a420ad441c..71c90ce7fc9 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -6714,11 +6714,12 @@ namespace ts {
                 const links = getSymbolLinks(symbol);
                 if (!links.lateSymbol && some(symbol.declarations, hasLateBindableName)) {
                     // force late binding of members/exports. This will set the late-bound symbol
+                    const parent = getMergedSymbol(symbol.parent)!;
                     if (some(symbol.declarations, hasStaticModifier)) {
-                        getExportsOfSymbol(symbol.parent!);
+                        getExportsOfSymbol(parent);
                     }
                     else {
-                        getMembersOfSymbol(symbol.parent!);
+                        getMembersOfSymbol(parent);
                     }
                 }
                 return links.lateSymbol || (links.lateSymbol = symbol);
diff --git a/src/testRunner/tsconfig.json b/src/testRunner/tsconfig.json
index d3ea4744e8a..6b73324e2f7 100644
--- a/src/testRunner/tsconfig.json
+++ b/src/testRunner/tsconfig.json
@@ -92,6 +92,7 @@
         "unittests/tsbuild/amdModulesWithOut.ts",
         "unittests/tsbuild/emptyFiles.ts",
         "unittests/tsbuild/graphOrdering.ts",
+        "unittests/tsbuild/lateBoundSymbol.ts",
         "unittests/tsbuild/missingExtendedFile.ts",
         "unittests/tsbuild/outFile.ts",
         "unittests/tsbuild/referencesWithRootDirInParent.ts",
diff --git a/src/testRunner/unittests/tsbuild/helpers.ts b/src/testRunner/unittests/tsbuild/helpers.ts
index 538ebd75cdb..589ba7a3021 100644
--- a/src/testRunner/unittests/tsbuild/helpers.ts
+++ b/src/testRunner/unittests/tsbuild/helpers.ts
@@ -285,8 +285,10 @@ Mismatch Actual(path, actual, expected): ${JSON.stringify(arrayFrom(mapDefinedIt
                     let newFs: vfs.FileSystem;
                     let actualReadFileMap: Map<number>;
                     let host: fakes.SolutionBuilderHost;
+                    let beforeBuildTime: number;
+                    let afterBuildTime: number;
                     before(() => {
-                        assert.equal(fs.statSync(lastProjectOutputJs).mtimeMs, firstBuildTime, "First build timestamp is correct");
+                        beforeBuildTime = fs.statSync(lastProjectOutputJs).mtimeMs;
                         tick();
                         newFs = fs.shadow();
                         tick();
@@ -298,13 +300,17 @@ Mismatch Actual(path, actual, expected): ${JSON.stringify(arrayFrom(mapDefinedIt
                             expectedBuildInfoFilesForSectionBaselines,
                             modifyFs: incrementalModifyFs,
                         }));
-                        assert.equal(newFs.statSync(lastProjectOutputJs).mtimeMs, time(), "Second build timestamp is correct");
+                        afterBuildTime = newFs.statSync(lastProjectOutputJs).mtimeMs;
                     });
                     after(() => {
                         newFs = undefined!;
                         actualReadFileMap = undefined!;
                         host = undefined!;
                     });
+                    it("verify build output times", () => {
+                        assert.equal(beforeBuildTime, firstBuildTime, "First build timestamp is correct");
+                        assert.equal(afterBuildTime, time(), "Second build timestamp is correct");
+                    });
                     if (!baselineOnly || verifyDiagnostics) {
                         it(`verify diagnostics`, () => {
                             host.assertDiagnosticMessages(...(incrementalExpectedDiagnostics || emptyArray));
diff --git a/src/testRunner/unittests/tsbuild/lateBoundSymbol.ts b/src/testRunner/unittests/tsbuild/lateBoundSymbol.ts
new file mode 100644
index 00000000000..ff9f1fc7c7a
--- /dev/null
+++ b/src/testRunner/unittests/tsbuild/lateBoundSymbol.ts
@@ -0,0 +1,47 @@
+namespace ts {
+    describe("unittests:: tsbuild:: lateBoundSymbol:: interface is merged and contains late bound member", () => {
+        let projFs: vfs.FileSystem;
+        const { time, tick } = getTime();
+        before(() => {
+            projFs = loadProjectFromDisk("tests/projects/lateBoundSymbol", time);
+        });
+        after(() => {
+            projFs = undefined!; // Release the contents
+        });
+
+        verifyTsbuildOutput({
+            scenario: "interface is merged and contains late bound member",
+            projFs: () => projFs,
+            time,
+            tick,
+            proj: "lateBoundSymbol",
+            rootNames: ["/src/tsconfig.json"],
+            expectedMapFileNames: emptyArray,
+            lastProjectOutputJs: "/src/src/main.js",
+            outputFiles: [
+                "/src/src/hkt.js",
+                "/src/src/main.js",
+                "/src/tsconfig.tsbuildinfo",
+            ],
+            initialBuild: {
+                modifyFs: noop,
+                expectedDiagnostics: [
+                    getExpectedDiagnosticForProjectsInBuild("src/tsconfig.json"),
+                    [Diagnostics.Project_0_is_out_of_date_because_output_file_1_does_not_exist, "src/tsconfig.json", "src/src/hkt.js"],
+                    [Diagnostics.Building_project_0, "/src/tsconfig.json"]
+                ]
+            },
+            incrementalDtsUnchangedBuild: {
+                modifyFs: fs => replaceText(fs, "/src/src/main.ts", "const x = 10;", ""),
+                expectedDiagnostics: [
+                    getExpectedDiagnosticForProjectsInBuild("src/tsconfig.json"),
+                    [Diagnostics.Project_0_is_out_of_date_because_oldest_output_1_is_older_than_newest_input_2, "src/tsconfig.json", "src/src/hkt.js", "src/src/main.ts"],
+                    [Diagnostics.Building_project_0, "/src/tsconfig.json"],
+                    [Diagnostics.Updating_unchanged_output_timestamps_of_project_0, "/src/tsconfig.json"]
+                ]
+            },
+            baselineOnly: true,
+            verifyDiagnostics: true
+        });
+    });
+}
diff --git a/tests/baselines/reference/tsbuild/lateBoundSymbol/incremental-declaration-doesnt-change/interface-is-merged-and-contains-late-bound-member.js b/tests/baselines/reference/tsbuild/lateBoundSymbol/incremental-declaration-doesnt-change/interface-is-merged-and-contains-late-bound-member.js
new file mode 100644
index 00000000000..89748694bbc
--- /dev/null
+++ b/tests/baselines/reference/tsbuild/lateBoundSymbol/incremental-declaration-doesnt-change/interface-is-merged-and-contains-late-bound-member.js
@@ -0,0 +1,113 @@
+//// [/src/src/main.js]
+"use strict";
+exports.__esModule = true;
+var sym = Symbol();
+
+
+//// [/src/src/main.ts]
+import { HKT } from "./hkt";
+
+const sym = Symbol();
+
+declare module "./hkt" {
+  interface HKT<T> {
+    [sym]: { a: T }
+  }
+}
+
+type A = HKT<number>[typeof sym];
+
+//// [/src/tsconfig.tsbuildinfo]
+{
+  "program": {
+    "fileInfos": {
+      "/lib/lib.es5.d.ts": {
+        "version": "/lib/lib.es5.d.ts",
+        "signature": "/lib/lib.es5.d.ts"
+      },
+      "/lib/lib.es2015.d.ts": {
+        "version": "/lib/lib.es2015.d.ts",
+        "signature": "/lib/lib.es2015.d.ts"
+      },
+      "/lib/lib.es2015.core.d.ts": {
+        "version": "/lib/lib.es2015.core.d.ts",
+        "signature": "/lib/lib.es2015.core.d.ts"
+      },
+      "/lib/lib.es2015.collection.d.ts": {
+        "version": "/lib/lib.es2015.collection.d.ts",
+        "signature": "/lib/lib.es2015.collection.d.ts"
+      },
+      "/lib/lib.es2015.generator.d.ts": {
+        "version": "/lib/lib.es2015.generator.d.ts",
+        "signature": "/lib/lib.es2015.generator.d.ts"
+      },
+      "/lib/lib.es2015.iterable.d.ts": {
+        "version": "/lib/lib.es2015.iterable.d.ts",
+        "signature": "/lib/lib.es2015.iterable.d.ts"
+      },
+      "/lib/lib.es2015.promise.d.ts": {
+        "version": "/lib/lib.es2015.promise.d.ts",
+        "signature": "/lib/lib.es2015.promise.d.ts"
+      },
+      "/lib/lib.es2015.proxy.d.ts": {
+        "version": "/lib/lib.es2015.proxy.d.ts",
+        "signature": "/lib/lib.es2015.proxy.d.ts"
+      },
+      "/lib/lib.es2015.reflect.d.ts": {
+        "version": "/lib/lib.es2015.reflect.d.ts",
+        "signature": "/lib/lib.es2015.reflect.d.ts"
+      },
+      "/lib/lib.es2015.symbol.d.ts": {
+        "version": "/lib/lib.es2015.symbol.d.ts",
+        "signature": "/lib/lib.es2015.symbol.d.ts"
+      },
+      "/lib/lib.es2015.symbol.wellknown.d.ts": {
+        "version": "/lib/lib.es2015.symbol.wellknown.d.ts",
+        "signature": "/lib/lib.es2015.symbol.wellknown.d.ts"
+      },
+      "/src/src/hkt.ts": {
+        "version": "675797797",
+        "signature": "2373810515"
+      },
+      "/src/src/main.ts": {
+        "version": "-27494779858",
+        "signature": "-7779857705"
+      }
+    },
+    "options": {
+      "rootDir": "/src/src",
+      "lib": [
+        "lib.es2015.d.ts"
+      ],
+      "incremental": true,
+      "configFilePath": "/src/tsconfig.json"
+    },
+    "referencedMap": {
+      "/src/src/main.ts": [
+        "/src/src/hkt.ts"
+      ]
+    },
+    "exportedModulesMap": {
+      "/src/src/main.ts": [
+        "/src/src/hkt.ts"
+      ]
+    },
+    "semanticDiagnosticsPerFile": [
+      "/lib/lib.es2015.collection.d.ts",
+      "/lib/lib.es2015.core.d.ts",
+      "/lib/lib.es2015.d.ts",
+      "/lib/lib.es2015.generator.d.ts",
+      "/lib/lib.es2015.iterable.d.ts",
+      "/lib/lib.es2015.promise.d.ts",
+      "/lib/lib.es2015.proxy.d.ts",
+      "/lib/lib.es2015.reflect.d.ts",
+      "/lib/lib.es2015.symbol.d.ts",
+      "/lib/lib.es2015.symbol.wellknown.d.ts",
+      "/lib/lib.es5.d.ts",
+      "/src/src/hkt.ts",
+      "/src/src/main.ts"
+    ]
+  },
+  "version": "FakeTSVersion"
+}
+
diff --git a/tests/baselines/reference/tsbuild/lateBoundSymbol/initial-Build/interface-is-merged-and-contains-late-bound-member.js b/tests/baselines/reference/tsbuild/lateBoundSymbol/initial-Build/interface-is-merged-and-contains-late-bound-member.js
new file mode 100644
index 00000000000..e30b62fcca8
--- /dev/null
+++ b/tests/baselines/reference/tsbuild/lateBoundSymbol/initial-Build/interface-is-merged-and-contains-late-bound-member.js
@@ -0,0 +1,106 @@
+//// [/src/src/hkt.js]
+"use strict";
+exports.__esModule = true;
+
+
+//// [/src/src/main.js]
+"use strict";
+exports.__esModule = true;
+var sym = Symbol();
+var x = 10;
+
+
+//// [/src/tsconfig.tsbuildinfo]
+{
+  "program": {
+    "fileInfos": {
+      "/lib/lib.es5.d.ts": {
+        "version": "/lib/lib.es5.d.ts",
+        "signature": "/lib/lib.es5.d.ts"
+      },
+      "/lib/lib.es2015.d.ts": {
+        "version": "/lib/lib.es2015.d.ts",
+        "signature": "/lib/lib.es2015.d.ts"
+      },
+      "/lib/lib.es2015.core.d.ts": {
+        "version": "/lib/lib.es2015.core.d.ts",
+        "signature": "/lib/lib.es2015.core.d.ts"
+      },
+      "/lib/lib.es2015.collection.d.ts": {
+        "version": "/lib/lib.es2015.collection.d.ts",
+        "signature": "/lib/lib.es2015.collection.d.ts"
+      },
+      "/lib/lib.es2015.generator.d.ts": {
+        "version": "/lib/lib.es2015.generator.d.ts",
+        "signature": "/lib/lib.es2015.generator.d.ts"
+      },
+      "/lib/lib.es2015.iterable.d.ts": {
+        "version": "/lib/lib.es2015.iterable.d.ts",
+        "signature": "/lib/lib.es2015.iterable.d.ts"
+      },
+      "/lib/lib.es2015.promise.d.ts": {
+        "version": "/lib/lib.es2015.promise.d.ts",
+        "signature": "/lib/lib.es2015.promise.d.ts"
+      },
+      "/lib/lib.es2015.proxy.d.ts": {
+        "version": "/lib/lib.es2015.proxy.d.ts",
+        "signature": "/lib/lib.es2015.proxy.d.ts"
+      },
+      "/lib/lib.es2015.reflect.d.ts": {
+        "version": "/lib/lib.es2015.reflect.d.ts",
+        "signature": "/lib/lib.es2015.reflect.d.ts"
+      },
+      "/lib/lib.es2015.symbol.d.ts": {
+        "version": "/lib/lib.es2015.symbol.d.ts",
+        "signature": "/lib/lib.es2015.symbol.d.ts"
+      },
+      "/lib/lib.es2015.symbol.wellknown.d.ts": {
+        "version": "/lib/lib.es2015.symbol.wellknown.d.ts",
+        "signature": "/lib/lib.es2015.symbol.wellknown.d.ts"
+      },
+      "/src/src/hkt.ts": {
+        "version": "675797797",
+        "signature": "2373810515"
+      },
+      "/src/src/main.ts": {
+        "version": "-28387946490",
+        "signature": "-7779857705"
+      }
+    },
+    "options": {
+      "rootDir": "/src/src",
+      "lib": [
+        "lib.es2015.d.ts"
+      ],
+      "incremental": true,
+      "configFilePath": "/src/tsconfig.json"
+    },
+    "referencedMap": {
+      "/src/src/main.ts": [
+        "/src/src/hkt.ts"
+      ]
+    },
+    "exportedModulesMap": {
+      "/src/src/main.ts": [
+        "/src/src/hkt.ts"
+      ]
+    },
+    "semanticDiagnosticsPerFile": [
+      "/lib/lib.es2015.collection.d.ts",
+      "/lib/lib.es2015.core.d.ts",
+      "/lib/lib.es2015.d.ts",
+      "/lib/lib.es2015.generator.d.ts",
+      "/lib/lib.es2015.iterable.d.ts",
+      "/lib/lib.es2015.promise.d.ts",
+      "/lib/lib.es2015.proxy.d.ts",
+      "/lib/lib.es2015.reflect.d.ts",
+      "/lib/lib.es2015.symbol.d.ts",
+      "/lib/lib.es2015.symbol.wellknown.d.ts",
+      "/lib/lib.es5.d.ts",
+      "/src/src/hkt.ts",
+      "/src/src/main.ts"
+    ]
+  },
+  "version": "FakeTSVersion"
+}
+
diff --git a/tests/baselines/reference/uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.js b/tests/baselines/reference/uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.js
new file mode 100644
index 00000000000..bfb6f0a29c7
--- /dev/null
+++ b/tests/baselines/reference/uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.js
@@ -0,0 +1,18 @@
+//// [uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts]
+const FOO_SYMBOL = Symbol('Foo');
+
+declare global {
+    interface Promise<T> {
+        [FOO_SYMBOL]?: number;
+    }
+}
+
+export function foo<T>(p: Promise<T>) {
+    p[FOO_SYMBOL] = 3;
+}
+
+//// [uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.js]
+const FOO_SYMBOL = Symbol('Foo');
+export function foo(p) {
+    p[FOO_SYMBOL] = 3;
+}
diff --git a/tests/baselines/reference/uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.symbols b/tests/baselines/reference/uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.symbols
new file mode 100644
index 00000000000..17af30e8fac
--- /dev/null
+++ b/tests/baselines/reference/uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.symbols
@@ -0,0 +1,29 @@
+=== tests/cases/compiler/uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts ===
+const FOO_SYMBOL = Symbol('Foo');
+>FOO_SYMBOL : Symbol(FOO_SYMBOL, Decl(uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts, 0, 5))
+>Symbol : Symbol(Symbol, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.symbol.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+
+declare global {
+>global : Symbol(global, Decl(uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts, 0, 33))
+
+    interface Promise<T> {
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts, 2, 16))
+>T : Symbol(T, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts, 3, 22))
+
+        [FOO_SYMBOL]?: number;
+>[FOO_SYMBOL] : Symbol(Promise[FOO_SYMBOL], Decl(uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts, 3, 26))
+>FOO_SYMBOL : Symbol(FOO_SYMBOL, Decl(uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts, 0, 5))
+    }
+}
+
+export function foo<T>(p: Promise<T>) {
+>foo : Symbol(foo, Decl(uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts, 6, 1))
+>T : Symbol(T, Decl(uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts, 8, 20))
+>p : Symbol(p, Decl(uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts, 8, 23))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts, 2, 16))
+>T : Symbol(T, Decl(uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts, 8, 20))
+
+    p[FOO_SYMBOL] = 3;
+>p : Symbol(p, Decl(uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts, 8, 23))
+>FOO_SYMBOL : Symbol(FOO_SYMBOL, Decl(uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts, 0, 5))
+}
diff --git a/tests/baselines/reference/uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.types b/tests/baselines/reference/uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.types
new file mode 100644
index 00000000000..62dcc0607ae
--- /dev/null
+++ b/tests/baselines/reference/uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.types
@@ -0,0 +1,28 @@
+=== tests/cases/compiler/uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts ===
+const FOO_SYMBOL = Symbol('Foo');
+>FOO_SYMBOL : unique symbol
+>Symbol('Foo') : unique symbol
+>Symbol : SymbolConstructor
+>'Foo' : "Foo"
+
+declare global {
+>global : any
+
+    interface Promise<T> {
+        [FOO_SYMBOL]?: number;
+>[FOO_SYMBOL] : number | undefined
+>FOO_SYMBOL : unique symbol
+    }
+}
+
+export function foo<T>(p: Promise<T>) {
+>foo : <T>(p: Promise<T>) => void
+>p : Promise<T>
+
+    p[FOO_SYMBOL] = 3;
+>p[FOO_SYMBOL] = 3 : 3
+>p[FOO_SYMBOL] : number | undefined
+>p : Promise<T>
+>FOO_SYMBOL : unique symbol
+>3 : 3
+}
diff --git a/tests/cases/compiler/uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts b/tests/cases/compiler/uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts
new file mode 100644
index 00000000000..f79c2a36e86
--- /dev/null
+++ b/tests/cases/compiler/uniqueSymbolAssignmentOnGlobalAugmentationSuceeds.ts
@@ -0,0 +1,13 @@
+// @strict: true
+// @target: es6
+const FOO_SYMBOL = Symbol('Foo');
+
+declare global {
+    interface Promise<T> {
+        [FOO_SYMBOL]?: number;
+    }
+}
+
+export function foo<T>(p: Promise<T>) {
+    p[FOO_SYMBOL] = 3;
+}
\ No newline at end of file
diff --git a/tests/projects/lateBoundSymbol/src/hkt.ts b/tests/projects/lateBoundSymbol/src/hkt.ts
new file mode 100644
index 00000000000..2b844a9ab79
--- /dev/null
+++ b/tests/projects/lateBoundSymbol/src/hkt.ts
@@ -0,0 +1 @@
+export interface HKT<T> { }
\ No newline at end of file
diff --git a/tests/projects/lateBoundSymbol/src/main.ts b/tests/projects/lateBoundSymbol/src/main.ts
new file mode 100644
index 00000000000..e5b5fcc6daa
--- /dev/null
+++ b/tests/projects/lateBoundSymbol/src/main.ts
@@ -0,0 +1,11 @@
+import { HKT } from "./hkt";
+
+const sym = Symbol();
+
+declare module "./hkt" {
+  interface HKT<T> {
+    [sym]: { a: T }
+  }
+}
+const x = 10;
+type A = HKT<number>[typeof sym];
\ No newline at end of file
diff --git a/tests/projects/lateBoundSymbol/tsconfig.json b/tests/projects/lateBoundSymbol/tsconfig.json
new file mode 100644
index 00000000000..78bf9e23f00
--- /dev/null
+++ b/tests/projects/lateBoundSymbol/tsconfig.json
@@ -0,0 +1,9 @@
+{
+  "compilerOptions": {
+    "rootDir": "src",
+    "lib": [
+      "es2015"
+    ],
+    "incremental": true
+  }
+}
\ No newline at end of file