diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 0b1e11db828..5142d608515 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -16936,6 +16936,7 @@ namespace ts {
         function checkNestedBlockScopedBinding(node: Identifier, symbol: Symbol): void {
             if (languageVersion >= ScriptTarget.ES2015 ||
                 (symbol.flags & (SymbolFlags.BlockScopedVariable | SymbolFlags.Class)) === 0 ||
+                isSourceFile(symbol.valueDeclaration) ||
                 symbol.valueDeclaration.parent.kind === SyntaxKind.CatchClause) {
                 return;
             }
@@ -29594,7 +29595,7 @@ namespace ts {
         }
 
         function isSymbolOfDeclarationWithCollidingName(symbol: Symbol): boolean {
-            if (symbol.flags & SymbolFlags.BlockScoped) {
+            if (symbol.flags & SymbolFlags.BlockScoped && !isSourceFile(symbol.valueDeclaration)) {
                 const links = getSymbolLinks(symbol);
                 if (links.isDeclarationWithCollidingName === undefined) {
                     const container = getEnclosingBlockScopeContainer(symbol.valueDeclaration);
diff --git a/tests/baselines/reference/checkMergedGlobalUMDSymbol.errors.txt b/tests/baselines/reference/checkMergedGlobalUMDSymbol.errors.txt
new file mode 100644
index 00000000000..f3d21e26b6e
--- /dev/null
+++ b/tests/baselines/reference/checkMergedGlobalUMDSymbol.errors.txt
@@ -0,0 +1,22 @@
+tests/cases/compiler/global.d.ts(6,16): error TS2403: Subsequent variable declarations must have the same type.  Variable 'THREE' must be of type 'typeof import("tests/cases/compiler/global")', but here has type 'typeof import("tests/cases/compiler/three")'.
+
+
+==== tests/cases/compiler/three.d.ts (0 errors) ====
+    export namespace THREE {
+      export class Vector2 {}
+    }
+    
+==== tests/cases/compiler/global.d.ts (1 errors) ====
+    import * as _three from './three';
+    
+    export as namespace THREE;
+    
+    declare global {
+      export const THREE: typeof _three;
+                   ~~~~~
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'THREE' must be of type 'typeof import("tests/cases/compiler/global")', but here has type 'typeof import("tests/cases/compiler/three")'.
+    }
+    
+==== tests/cases/compiler/test.ts (0 errors) ====
+    const m = THREE
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/checkMergedGlobalUMDSymbol.js b/tests/baselines/reference/checkMergedGlobalUMDSymbol.js
new file mode 100644
index 00000000000..c3a3ed6fb8a
--- /dev/null
+++ b/tests/baselines/reference/checkMergedGlobalUMDSymbol.js
@@ -0,0 +1,22 @@
+//// [tests/cases/compiler/checkMergedGlobalUMDSymbol.ts] ////
+
+//// [three.d.ts]
+export namespace THREE {
+  export class Vector2 {}
+}
+
+//// [global.d.ts]
+import * as _three from './three';
+
+export as namespace THREE;
+
+declare global {
+  export const THREE: typeof _three;
+}
+
+//// [test.ts]
+const m = THREE
+
+
+//// [test.js]
+var m = THREE;
diff --git a/tests/baselines/reference/checkMergedGlobalUMDSymbol.symbols b/tests/baselines/reference/checkMergedGlobalUMDSymbol.symbols
new file mode 100644
index 00000000000..72038e964b6
--- /dev/null
+++ b/tests/baselines/reference/checkMergedGlobalUMDSymbol.symbols
@@ -0,0 +1,28 @@
+=== tests/cases/compiler/three.d.ts ===
+export namespace THREE {
+>THREE : Symbol(THREE, Decl(three.d.ts, 0, 0))
+
+  export class Vector2 {}
+>Vector2 : Symbol(Vector2, Decl(three.d.ts, 0, 24))
+}
+
+=== tests/cases/compiler/global.d.ts ===
+import * as _three from './three';
+>_three : Symbol(_three, Decl(global.d.ts, 0, 6))
+
+export as namespace THREE;
+>THREE : Symbol(THREE, Decl(global.d.ts, 0, 34))
+
+declare global {
+>global : Symbol(global, Decl(global.d.ts, 2, 26))
+
+  export const THREE: typeof _three;
+>THREE : Symbol("tests/cases/compiler/global", Decl(global.d.ts, 0, 0), Decl(global.d.ts, 5, 14))
+>_three : Symbol(_three, Decl(global.d.ts, 0, 6))
+}
+
+=== tests/cases/compiler/test.ts ===
+const m = THREE
+>m : Symbol(m, Decl(test.ts, 0, 5))
+>THREE : Symbol("tests/cases/compiler/global", Decl(global.d.ts, 0, 0), Decl(global.d.ts, 5, 14))
+
diff --git a/tests/baselines/reference/checkMergedGlobalUMDSymbol.types b/tests/baselines/reference/checkMergedGlobalUMDSymbol.types
new file mode 100644
index 00000000000..eeb5ce22501
--- /dev/null
+++ b/tests/baselines/reference/checkMergedGlobalUMDSymbol.types
@@ -0,0 +1,28 @@
+=== tests/cases/compiler/three.d.ts ===
+export namespace THREE {
+>THREE : typeof THREE
+
+  export class Vector2 {}
+>Vector2 : Vector2
+}
+
+=== tests/cases/compiler/global.d.ts ===
+import * as _three from './three';
+>_three : typeof _three
+
+export as namespace THREE;
+>THREE : typeof import("tests/cases/compiler/global")
+
+declare global {
+>global : typeof global
+
+  export const THREE: typeof _three;
+>THREE : typeof import("tests/cases/compiler/global")
+>_three : typeof _three
+}
+
+=== tests/cases/compiler/test.ts ===
+const m = THREE
+>m : typeof import("tests/cases/compiler/global")
+>THREE : typeof import("tests/cases/compiler/global")
+
diff --git a/tests/cases/compiler/checkMergedGlobalUMDSymbol.ts b/tests/cases/compiler/checkMergedGlobalUMDSymbol.ts
new file mode 100644
index 00000000000..9edddd7a64b
--- /dev/null
+++ b/tests/cases/compiler/checkMergedGlobalUMDSymbol.ts
@@ -0,0 +1,16 @@
+// @Filename: three.d.ts
+export namespace THREE {
+  export class Vector2 {}
+}
+
+// @Filename: global.d.ts
+import * as _three from './three';
+
+export as namespace THREE;
+
+declare global {
+  export const THREE: typeof _three;
+}
+
+// @Filename: test.ts
+const m = THREE