diff --git a/src/core/budgetManager.ts b/src/core/budgetManager.ts
index af4b96f..9f2b703 100644
--- a/src/core/budgetManager.ts
+++ b/src/core/budgetManager.ts
@@ -11,7 +11,7 @@ export class BudgetManager {
 
   constructor(options: BudgetGuardOptions) {
     // Validate monthly limit
-    if (typeof options.monthlyLimit !== 'number' || isNaN(options.monthlyLimit) || !isFinite(options.monthlyLimit)) {
+    if (typeof options.monthlyLimit !== 'number' || Number.isNaN(options.monthlyLimit) || !isFinite(options.monthlyLimit)) {
       throw new Error('TokenFirewall: monthlyLimit must be a valid number');
     }
 
@@ -36,7 +36,7 @@ export class BudgetManager {
    */
   public async track(cost: number): Promise<void> {
     // Validate cost parameter
-    if (typeof cost !== 'number' || isNaN(cost) || !isFinite(cost)) {
+    if (typeof cost !== 'number' || Number.isNaN(cost) || !isFinite(cost)) {
       throw new Error('TokenFirewall: Cost must be a valid number');
     }
 
@@ -116,7 +116,7 @@ export class BudgetManager {
    */
   public importState(state: { totalSpent: number }): void {
     // Validate totalSpent
-    if (typeof state.totalSpent !== 'number' || isNaN(state.totalSpent) || !isFinite(state.totalSpent)) {
+    if (typeof state.totalSpent !== 'number' || Number.isNaN(state.totalSpent) || !isFinite(state.totalSpent)) {
       throw new Error('TokenFirewall: Invalid budget state - totalSpent must be a valid number');
     }
 
diff --git a/src/index.ts b/src/index.ts
index c769e99..0217095 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -66,10 +66,10 @@ export function registerPricing(provider: string, model: string, pricing: ModelP
   if (!pricing || typeof pricing !== 'object') {
     throw new Error('TokenFirewall: Pricing must be an object');
   }
-  if (typeof pricing.input !== 'number' || pricing.input < 0 || !isFinite(pricing.input) || isNaN(pricing.input)) {
+  if (typeof pricing.input !== 'number' || pricing.input < 0 || !isFinite(pricing.input) || Number.isNaN(pricing.input)) {
     throw new Error('TokenFirewall: Pricing input must be a non-negative finite number');
   }
-  if (typeof pricing.output !== 'number' || pricing.output < 0 || !isFinite(pricing.output) || isNaN(pricing.output)) {
+  if (typeof pricing.output !== 'number' || pricing.output < 0 || !isFinite(pricing.output) || Number.isNaN(pricing.output)) {
     throw new Error('TokenFirewall: Pricing output must be a non-negative finite number');
   }
 
@@ -90,7 +90,7 @@ export function registerContextLimit(provider: string, model: string, contextLim
   if (!model || typeof model !== 'string' || model.trim() === '') {
     throw new Error('TokenFirewall: Model must be a non-empty string');
   }
-  if (typeof contextLimit !== 'number' || contextLimit <= 0 || !isFinite(contextLimit) || isNaN(contextLimit)) {
+  if (typeof contextLimit !== 'number' || contextLimit <= 0 || !isFinite(contextLimit) || Number.isNaN(contextLimit)) {
     throw new Error('TokenFirewall: Context limit must be a positive finite number');
   }