diff --git a/src/LuaTransformer.ts b/src/LuaTransformer.ts
index d1fd6226e..4e386daa2 100644
--- a/src/LuaTransformer.ts
+++ b/src/LuaTransformer.ts
@@ -1585,6 +1585,13 @@ export class LuaTransformer {
 
         const symbol = this.checker.getSymbolAtLocation(statement.name);
         const hasExports = symbol !== undefined && this.checker.getExportsOfModule(symbol).length > 0;
+        const nameIdentifier = this.transformIdentifier(statement.name as ts.Identifier);
+        const exportScope = this.getIdentifierExportScope(nameIdentifier);
+
+        // Non-module namespace could be merged if:
+        // - is top level
+        // - is nested and exported
+        const isNonModuleMergeable = !this.isModule && (!this.currentNamespace || exportScope);
 
         // This is NOT the first declaration if:
         // - declared as a module before this (ignore interfaces with same name)
@@ -1594,9 +1601,19 @@ export class LuaTransformer {
             (symbol.declarations.findIndex(d => ts.isClassLike(d) || ts.isFunctionDeclaration(d)) === -1 &&
                 statement === symbol.declarations.find(ts.isModuleDeclaration));
 
-        const nameIdentifier = this.transformIdentifier(statement.name as ts.Identifier);
+        if (isNonModuleMergeable) {
+            // 'local NS = NS or {}' or 'exportTable.NS = exportTable.NS or {}'
+            const localDeclaration = this.createLocalOrExportedOrGlobalDeclaration(
+                nameIdentifier,
+                tstl.createBinaryExpression(
+                    this.addExportToIdentifier(nameIdentifier),
+                    tstl.createTableExpression(),
+                    tstl.SyntaxKind.OrOperator
+                )
+            );
 
-        if (isFirstDeclaration) {
+            result.push(...localDeclaration);
+        } else if (isFirstDeclaration) {
             // local NS = {} or exportTable.NS = {}
             const localDeclaration = this.createLocalOrExportedOrGlobalDeclaration(
                 nameIdentifier,
@@ -1604,17 +1621,21 @@ export class LuaTransformer {
             );
 
             result.push(...localDeclaration);
+        }
 
-            const exportScope = this.getIdentifierExportScope(nameIdentifier);
-            if (exportScope && hasExports && tsHelper.moduleHasEmittedBody(statement)) {
-                // local NS = exportTable.NS
-                const localDeclaration = this.createHoistableVariableDeclarationStatement(
-                    this.createModuleLocalNameIdentifier(statement),
-                    this.createExportedIdentifier(nameIdentifier, exportScope)
-                );
+        if (
+            (isNonModuleMergeable || isFirstDeclaration) &&
+            exportScope &&
+            hasExports &&
+            tsHelper.moduleHasEmittedBody(statement)
+        ) {
+            // local NS = exportTable.NS
+            const localDeclaration = this.createHoistableVariableDeclarationStatement(
+                this.createModuleLocalNameIdentifier(statement),
+                this.createExportedIdentifier(nameIdentifier, exportScope)
+            );
 
-                result.push(localDeclaration);
-            }
+            result.push(localDeclaration);
         }
 
         // Set current namespace for nested NS
diff --git a/test/translation/__snapshots__/transformation.spec.ts.snap b/test/translation/__snapshots__/transformation.spec.ts.snap
index 58e99b895..a41b2d6dc 100644
--- a/test/translation/__snapshots__/transformation.spec.ts.snap
+++ b/test/translation/__snapshots__/transformation.spec.ts.snap
@@ -471,7 +471,7 @@ end
 return ____exports"
 `;
 
-exports[`Transformation (modulesNamespaceNoExport) 1`] = `"TestSpace = {}"`;
+exports[`Transformation (modulesNamespaceNoExport) 1`] = `"TestSpace = TestSpace or {}"`;
 
 exports[`Transformation (modulesNamespaceWithMemberExport) 1`] = `
 "local ____exports = {}
@@ -503,7 +503,7 @@ return ____exports"
 exports[`Transformation (modulesVariableNoExport) 1`] = `"local foo = \\"bar\\""`;
 
 exports[`Transformation (namespace) 1`] = `
-"myNamespace = {}
+"myNamespace = myNamespace or {}
 do
     local function nsMember(self)
     end
@@ -537,6 +537,7 @@ function MergedClass.prototype.methodB(self)
     self:methodA()
     self:propertyFunc()
 end
+MergedClass = MergedClass or {}
 do
     function MergedClass.namespaceFunc(self)
     end
@@ -549,7 +550,7 @@ MergedClass:namespaceFunc()"
 `;
 
 exports[`Transformation (namespaceNested) 1`] = `
-"myNamespace = {}
+"myNamespace = myNamespace or {}
 do
     local myNestedNamespace = {}
     do
diff --git a/test/unit/modules.spec.ts b/test/unit/modules.spec.ts
index 8b52cfc1c..5134067b7 100644
--- a/test/unit/modules.spec.ts
+++ b/test/unit/modules.spec.ts
@@ -160,3 +160,23 @@ test("Module merged with interface", () => {
     const code = `return Foo.bar();`;
     expect(util.transpileAndExecute(code, undefined, undefined, header)).toBe("foobar");
 });
+
+test("module merged across files", () => {
+    const testA = `
+        namespace NS {
+            export namespace Inner {
+                export const foo = "foo";
+            }
+        }
+    `;
+    const testB = `
+        namespace NS {
+            export namespace Inner {
+                export const bar = "bar";
+            }
+        }
+    `;
+    const { transpiledFiles } = util.transpileStringsAsProject({ "testA.ts": testA, "testB.ts": testB });
+    const lua = transpiledFiles.map(f => f.lua).join("\n") + "\nreturn NS.Inner.foo .. NS.Inner.bar";
+    expect(util.executeLua(lua)).toBe("foobar");
+});
diff --git a/test/util.ts b/test/util.ts
index 3da13b395..6c314780b 100644
--- a/test/util.ts
+++ b/test/util.ts
@@ -20,10 +20,10 @@ export function transpileString(
     return file.lua.trim();
 }
 
-export function transpileStringResult(
-    input: string | Record<string, string>,
+export function transpileStringsAsProject(
+    input: Record<string, string>,
     options: tstl.CompilerOptions = {}
-): Required<tstl.TranspileStringResult> {
+): tstl.TranspileResult {
     const optionsWithDefaults = {
         luaTarget: tstl.LuaTarget.Lua53,
         noHeader: true,
@@ -34,9 +34,16 @@ export function transpileStringResult(
         ...options,
     };
 
-    const { diagnostics, transpiledFiles } = tstl.transpileVirtualProject(
+    return tstl.transpileVirtualProject(input, optionsWithDefaults);
+}
+
+export function transpileStringResult(
+    input: string | Record<string, string>,
+    options: tstl.CompilerOptions = {}
+): Required<tstl.TranspileStringResult> {
+    const { diagnostics, transpiledFiles } = transpileStringsAsProject(
         typeof input === "string" ? { "main.ts": input } : input,
-        optionsWithDefaults
+        options
     );
 
     const file = transpiledFiles.find(({ fileName }) => /\bmain\.[a-z]+$/.test(fileName));