diff --git a/scripts/copyMetafiles.js b/scripts/copyMetafiles.js
index d14964f1c..6140bd2dc 100644
--- a/scripts/copyMetafiles.js
+++ b/scripts/copyMetafiles.js
@@ -8,11 +8,11 @@ const files = [
   '.nycrc',
 ];
 
-const directories = [
+const directories = [].concat(
   'memo-parser',
-  ...resolverDirectories,
+  resolverDirectories,
   'utils',
-];
+);
 
 for (const directory of directories) {
   for (const file of files) {
diff --git a/src/rules/export.js b/src/rules/export.js
index da0df1ee7..92583bdd8 100644
--- a/src/rules/export.js
+++ b/src/rules/export.js
@@ -37,7 +37,6 @@ const tsTypePrefix = 'type:';
  */
 function isTypescriptFunctionOverloads(nodes) {
   const nodesArr = Array.from(nodes);
-  const types = new Set(nodesArr.map(node => node.parent.type));
 
   const idents = flatMap(nodesArr, (node) => (
     node.declaration && (
@@ -51,6 +50,7 @@ function isTypescriptFunctionOverloads(nodes) {
     return true;
   }
 
+  const types = new Set(nodesArr.map(node => node.parent.type));
   if (!types.has('TSDeclareFunction')) {
     return false;
   }
diff --git a/src/rules/no-namespace.js b/src/rules/no-namespace.js
index 4382007a5..a078137e6 100644
--- a/src/rules/no-namespace.js
+++ b/src/rules/no-namespace.js
@@ -144,10 +144,7 @@ function getVariableNamesInScope(scopeManager, node) {
     currentNode = currentNode.parent;
     scope = scopeManager.acquire(currentNode, true);
   }
-  return new Set([
-    ...scope.variables.map(variable => variable.name),
-    ...scope.upper.variables.map(variable => variable.name),
-  ]);
+  return new Set(scope.variables.concat(scope.upper.variables).map(variable => variable.name));
 }
 
 /**
diff --git a/tests/src/rules/consistent-type-specifier-style.js b/tests/src/rules/consistent-type-specifier-style.js
index 31a4c09ff..440ef3aff 100644
--- a/tests/src/rules/consistent-type-specifier-style.js
+++ b/tests/src/rules/consistent-type-specifier-style.js
@@ -367,14 +367,14 @@ context('TypeScript', () => {
     },
   });
   ruleTester.run('consistent-type-specifier-style', rule, {
-    valid: [
-      ...COMMON_TESTS.valid,
-      ...TS_ONLY.valid,
-    ],
-    invalid: [
-      ...COMMON_TESTS.invalid,
-      ...TS_ONLY.invalid,
-    ],
+    valid: [].concat(
+      COMMON_TESTS.valid,
+      TS_ONLY.valid,
+    ),
+    invalid: [].concat(
+      COMMON_TESTS.invalid,
+      TS_ONLY.invalid,
+    ),
   });
 });
 
@@ -391,13 +391,13 @@ context('Babel/Flow', () => {
     },
   });
   ruleTester.run('consistent-type-specifier-style', rule, {
-    valid: [
-      ...COMMON_TESTS.valid,
-      ...FLOW_ONLY.valid,
-    ],
-    invalid: [
-      ...COMMON_TESTS.invalid,
-      ...FLOW_ONLY.invalid,
-    ],
+    valid: [].concat(
+      COMMON_TESTS.valid,
+      FLOW_ONLY.valid,
+    ),
+    invalid: [].concat(
+      COMMON_TESTS.invalid,
+      FLOW_ONLY.invalid,
+    ),
   });
 });