diff --git a/packages/eslint-plugin/tests/rules/no-use-before-define.test.ts b/packages/eslint-plugin/tests/rules/no-use-before-define.test.ts
index ad66ff7858e..23f2abb0473 100644
--- a/packages/eslint-plugin/tests/rules/no-use-before-define.test.ts
+++ b/packages/eslint-plugin/tests/rules/no-use-before-define.test.ts
@@ -347,6 +347,17 @@ const React = require('react');
     `
 type T = (value: unknown) => value is Id;
     `,
+    `
+global.foo = true;
+
+declare global {
+  namespace NodeJS {
+    interface Global {
+      foo?: boolean;
+    }
+  }
+}
+    `,
   ],
   invalid: [
     {
diff --git a/packages/scope-manager/src/referencer/Referencer.ts b/packages/scope-manager/src/referencer/Referencer.ts
index 6cccab10428..56c974055bc 100644
--- a/packages/scope-manager/src/referencer/Referencer.ts
+++ b/packages/scope-manager/src/referencer/Referencer.ts
@@ -765,7 +765,7 @@ class Referencer extends Visitor {
   }
 
   protected TSModuleDeclaration(node: TSESTree.TSModuleDeclaration): void {
-    if (node.id.type === AST_NODE_TYPES.Identifier) {
+    if (node.id.type === AST_NODE_TYPES.Identifier && !node.global) {
       this.currentScope().defineIdentifier(
         node.id,
         new TSModuleNameDefinition(node.id, node),
diff --git a/packages/scope-manager/tests/fixtures/ts-module/global-augmentation.ts b/packages/scope-manager/tests/fixtures/ts-module/global-augmentation.ts
new file mode 100644
index 00000000000..078de28ca2f
--- /dev/null
+++ b/packages/scope-manager/tests/fixtures/ts-module/global-augmentation.ts
@@ -0,0 +1,3 @@
+//// @sourceType = module
+
+declare global {}
diff --git a/packages/scope-manager/tests/fixtures/ts-module/global-augmentation.ts.shot b/packages/scope-manager/tests/fixtures/ts-module/global-augmentation.ts.shot
new file mode 100644
index 00000000000..4a93b639545
--- /dev/null
+++ b/packages/scope-manager/tests/fixtures/ts-module/global-augmentation.ts.shot
@@ -0,0 +1,42 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`ts-module global-augmentation 1`] = `
+ScopeManager {
+  variables: Array [
+    ImplicitGlobalConstTypeVariable,
+  ],
+  scopes: Array [
+    GlobalScope$1 {
+      block: Program$1,
+      isStrict: false,
+      references: Array [],
+      set: Map {
+        "const" => ImplicitGlobalConstTypeVariable,
+      },
+      type: "global",
+      upper: null,
+      variables: Array [
+        ImplicitGlobalConstTypeVariable,
+      ],
+    },
+    ModuleScope$2 {
+      block: Program$1,
+      isStrict: true,
+      references: Array [],
+      set: Map {},
+      type: "module",
+      upper: GlobalScope$1,
+      variables: Array [],
+    },
+    TSModuleScope$3 {
+      block: TSModuleDeclaration$2,
+      isStrict: true,
+      references: Array [],
+      set: Map {},
+      type: "tsModule",
+      upper: ModuleScope$2,
+      variables: Array [],
+    },
+  ],
+}
+`;