diff --git a/backend/src/config/validate.spec.ts b/backend/src/config/validate.spec.ts
new file mode 100644
index 0000000..e81a0f5
--- /dev/null
+++ b/backend/src/config/validate.spec.ts
@@ -0,0 +1,37 @@
+import 'reflect-metadata';
+import { validate } from './validate';
+
+const validConfig = (overrides: Record<string, unknown> = {}): Record<string, unknown> => ({
+    NODE_ENV: 'development',
+    BACKEND_PORT: 3000,
+    POSTGRES_USER: 'postgres',
+    POSTGRES_PASSWORD: 'postgres',
+    POSTGRES_DB: 'private_image',
+    POSTGRES_HOST: 'postgres',
+    POSTGRES_PORT: 5432,
+    POSTGRES_MIGRATIONS_RUN: 'false',
+    CORS_ORIGINS: 'http://localhost:5173',
+    MAX_IMAGES_PER_UPLOAD: 10,
+    MULTER_MAX_FILE_BYTES: 10485760,
+    ALTCHA_ENABLED: 'true',
+    ALTCHA_HMAC_KEY: 'secret',
+    ALTCHA_MAX_NUMBER: 50000,
+    NEVER_MODE_INACTIVITY_DAYS: 365,
+    THROTTLE_TTL_MS: 60000,
+    THROTTLE_LIMIT: 1000,
+    THROTTLE_UPLOAD_TTL_MS: 60000,
+    THROTTLE_UPLOAD_LIMIT: 20,
+    ...overrides
+});
+
+describe('validate', () => {
+    it('accepts true and false env boolean strings', () => {
+        expect(() => validate(validConfig({ POSTGRES_MIGRATIONS_RUN: 'true' }))).not.toThrow();
+        expect(() => validate(validConfig({ ALTCHA_ENABLED: 'false' }))).not.toThrow();
+    });
+
+    it('rejects non-literal boolean env values', () => {
+        expect(() => validate(validConfig({ ALTCHA_ENABLED: 'yes' }))).toThrow();
+        expect(() => validate(validConfig({ POSTGRES_MIGRATIONS_RUN: '1' }))).toThrow();
+    });
+});
diff --git a/backend/src/config/validate.ts b/backend/src/config/validate.ts
index f95945d..65923e9 100644
--- a/backend/src/config/validate.ts
+++ b/backend/src/config/validate.ts
@@ -1,5 +1,7 @@
 import { plainToClass } from 'class-transformer';
-import { IsBoolean, IsEnum, IsNotEmpty, IsNumber, IsString, Max, Min, validateSync } from 'class-validator';
+import { IsEnum, IsIn, IsNotEmpty, IsNumber, IsString, Max, Min, validateSync } from 'class-validator';
+import { BOOLEAN_STRING_VALUES } from '../consts/booleanStringValues';
+import type { BooleanStringValue } from '../types/BooleanStringValue';
 import { NodeEnv } from '../types/NodeEnv';
 
 class EnvironmentVariables {
@@ -36,8 +38,8 @@ class EnvironmentVariables {
     POSTGRES_PORT: number;
 
     @IsNotEmpty()
-    @IsBoolean()
-    POSTGRES_MIGRATIONS_RUN: boolean;
+    @IsIn(BOOLEAN_STRING_VALUES)
+    POSTGRES_MIGRATIONS_RUN: BooleanStringValue;
 
     @IsNotEmpty()
     @IsString()
@@ -56,8 +58,8 @@ class EnvironmentVariables {
     MULTER_MAX_FILE_BYTES: number;
 
     @IsNotEmpty()
-    @IsBoolean()
-    ALTCHA_ENABLED: boolean;
+    @IsIn(BOOLEAN_STRING_VALUES)
+    ALTCHA_ENABLED: BooleanStringValue;
 
     @IsNotEmpty()
     @IsString()
diff --git a/backend/src/consts/booleanStringValues.ts b/backend/src/consts/booleanStringValues.ts
new file mode 100644
index 0000000..309c04f
--- /dev/null
+++ b/backend/src/consts/booleanStringValues.ts
@@ -0,0 +1 @@
+export const BOOLEAN_STRING_VALUES = ['true', 'false'] as const;
diff --git a/backend/src/types/BooleanStringValue.ts b/backend/src/types/BooleanStringValue.ts
new file mode 100644
index 0000000..40237ab
--- /dev/null
+++ b/backend/src/types/BooleanStringValue.ts
@@ -0,0 +1,3 @@
+import { BOOLEAN_STRING_VALUES } from '../consts/booleanStringValues';
+
+export type BooleanStringValue = (typeof BOOLEAN_STRING_VALUES)[number];