diff --git a/tsc/internal/execute/incremental/programtosnapshot.go b/tsc/internal/execute/incremental/programtosnapshot.go
index 14f7b99fc1815..6b7d558cf971d 100644
--- a/tsc/internal/execute/incremental/programtosnapshot.go
+++ b/tsc/internal/execute/incremental/programtosnapshot.go
@@ -260,6 +260,10 @@ func (t *toProgramSnapshot) handlePendingCheck() {
 
 func fileAffectsGlobalScope(file *ast.SourceFile) bool {
 	binder.BindSourceFile(file)
+	// UMD exports introduce global names even though the file is an external module.
+	if len(file.GlobalExports) > 0 {
+		return true
+	}
 	// if file contains anything that augments to global scope we need to build them as if
 	// they are global files as well as module
 	if core.Some(file.ModuleAugmentations, func(augmentation *ast.ModuleName) bool {
diff --git a/tsc/internal/execute/tsctests/umd_test.go b/tsc/internal/execute/tsctests/umd_test.go
new file mode 100644
index 0000000000000..1c8252c142fc6
--- /dev/null
+++ b/tsc/internal/execute/tsctests/umd_test.go
@@ -0,0 +1,72 @@
+package tsctests
+
+import "testing"
+
+func TestTscUMD(t *testing.T) {
+	t.Parallel()
+	for _, args := range [][]string{nil, {"--watch"}} {
+		const umdPath = "/home/src/workspaces/project/umd.d.ts"
+		const present = "export as namespace UmdApi;\nexport interface Item { value: number }\n"
+		(&tscInput{
+			subScenario:     "UMD global export changes invalidate unchanged consumers",
+			commandLineArgs: args,
+			files: FileMap{
+				"/home/src/workspaces/project/tsconfig.json": `{"compilerOptions":{"strict":true,"incremental":true,"noEmit":true,"types":[]},"include":["*.ts"]}`,
+				umdPath:                                  present,
+				"/home/src/workspaces/project/client.ts": "declare const item: UmdApi.Item;\nconst checked: number = item.value;\n",
+			},
+			edits: []*tscEdit{
+				noChange,
+				{
+					caption: "remove the global namespace export",
+					edit: func(sys *TestSys) {
+						sys.writeFileNoError(umdPath, "export interface Item { value: number }\n")
+					},
+				},
+				{
+					caption: "restore the global namespace export",
+					edit: func(sys *TestSys) {
+						sys.writeFileNoError(umdPath, present)
+					},
+				},
+				{
+					caption: "rename the global namespace export",
+					edit: func(sys *TestSys) {
+						sys.replaceFileText(umdPath, "UmdApi", "OtherApi")
+					},
+				},
+				{
+					caption: "restore the global namespace name",
+					edit: func(sys *TestSys) {
+						sys.writeFileNoError(umdPath, present)
+					},
+				},
+				{
+					caption: "make the exported property incompatible",
+					edit: func(sys *TestSys) {
+						sys.replaceFileText(umdPath, "value: number", "value: string")
+					},
+				},
+				{
+					caption: "restore the exported property type",
+					edit: func(sys *TestSys) {
+						sys.writeFileNoError(umdPath, present)
+					},
+				},
+				{
+					caption: "delete the UMD declaration file",
+					edit: func(sys *TestSys) {
+						sys.removeNoError(umdPath)
+					},
+				},
+				{
+					caption: "restore the UMD declaration file",
+					edit: func(sys *TestSys) {
+						sys.writeFileNoError(umdPath, present)
+					},
+				},
+				noChange,
+			},
+		}).run(t, "umd")
+	}
+}