diff --git a/src/rules/noDuplicateVariableRule.ts b/src/rules/noDuplicateVariableRule.ts
index cef34a8cc65..8bce94b79c3 100644
--- a/src/rules/noDuplicateVariableRule.ts
+++ b/src/rules/noDuplicateVariableRule.ts
@@ -63,7 +63,7 @@ export class Rule extends Lint.Rules.AbstractRule {
 }
 
 class NoDuplicateVariableWalker extends Lint.AbstractWalker<Options> {
-    private scope: Set<string>;
+    private scope: Set<string> = new Set();
     public walk(sourceFile: ts.SourceFile) {
         this.scope = new Set();
         const cb = (node: ts.Node): void => {
diff --git a/src/rules/noShadowedVariableRule.ts b/src/rules/noShadowedVariableRule.ts
index b29c999308c..0f4af2f49ba 100644
--- a/src/rules/noShadowedVariableRule.ts
+++ b/src/rules/noShadowedVariableRule.ts
@@ -150,7 +150,7 @@ class Scope {
 }
 
 class NoShadowedVariableWalker extends Lint.AbstractWalker<Options> {
-    private scope: Scope;
+    private scope: Scope = new Scope();
     public walk(sourceFile: ts.SourceFile) {
         if (sourceFile.isDeclarationFile) {
             return;
diff --git a/src/rules/preferConstRule.ts b/src/rules/preferConstRule.ts
index 984f95dd782..9c15345fb91 100644
--- a/src/rules/preferConstRule.ts
+++ b/src/rules/preferConstRule.ts
@@ -121,7 +121,7 @@ interface DestructuringInfo {
 }
 
 class PreferConstWalker extends Lint.AbstractWalker<Options> {
-    private scope: Scope;
+    private scope: Scope = new Scope();
     public walk(sourceFile: ts.SourceFile) {
         // don't check anything on declaration files
         if (sourceFile.isDeclarationFile) {
diff --git a/src/tsconfig.json b/src/tsconfig.json
index 319e241f1e4..c410e416125 100644
--- a/src/tsconfig.json
+++ b/src/tsconfig.json
@@ -8,6 +8,7 @@
         "noUnusedLocals": true,
         "strictNullChecks": true,
         "strictFunctionTypes": true,
+        "strictPropertyInitialization": true,
         "importHelpers": true,
         "declaration": true,
         "sourceMap": false,
diff --git a/test/tsconfig.json b/test/tsconfig.json
index d9458ba5b48..772bb2cb5d8 100644
--- a/test/tsconfig.json
+++ b/test/tsconfig.json
@@ -8,6 +8,7 @@
         "noUnusedLocals": true,
         "strictNullChecks": true,
         "strictFunctionTypes": true,
+        "strictPropertyInitialization": true,
         "sourceMap": true,
         "target": "es5",
         "lib": ["es6"],