diff --git a/lib/optimize/ModuleConcatenationPlugin.js b/lib/optimize/ModuleConcatenationPlugin.js
index 97e23e02b..24710016f 100644
--- a/lib/optimize/ModuleConcatenationPlugin.js
+++ b/lib/optimize/ModuleConcatenationPlugin.js
@@ -321,29 +321,27 @@ class ModuleConcatenationPlugin {
 	}
 
 	getImports(module) {
-		return Array.from(
-			new Set(
-				module.dependencies
+		return new Set(
+			module.dependencies
 
-					// Only harmony Dependencies
-					.filter(dep => dep instanceof HarmonyImportDependency)
+				// Get reference info only for harmony Dependencies
+				.map(
+					dep =>
+						dep instanceof HarmonyImportDependency ? dep.getReference() : null
+				)
 
-					// Get reference info for this dependency
-					.map(dep => dep.getReference())
+				// Reference is valid and has a module
+				// Dependencies are simple enough to concat them
+				.filter(
+					ref =>
+						ref &&
+						ref.module &&
+						(Array.isArray(ref.importedNames) ||
+							Array.isArray(ref.module.buildMeta.providedExports))
+				)
 
-					// Reference is valid and has a module
-					.filter(ref => ref && ref.module)
-
-					// Dependencies are simple enough to concat them
-					.filter(
-						ref =>
-							Array.isArray(ref.importedNames) ||
-							Array.isArray(ref.module.buildMeta.providedExports)
-					)
-
-					// Take the imported module
-					.map(ref => ref.module)
-			)
+				// Take the imported module
+				.map(ref => ref.module)
 		);
 	}