diff --git a/packages/config-loader/src/loader.test.ts b/packages/config-loader/src/loader.test.ts
index 66894c7dec..4a7c9f238c 100644
--- a/packages/config-loader/src/loader.test.ts
+++ b/packages/config-loader/src/loader.test.ts
@@ -30,6 +30,14 @@ jest.mock('fs-extra', () => {
         sessionKey: development-key
     `,
     '/root/secrets/session-key.txt': 'abc123',
+    '/secret-port/app-config.yaml': `
+      backend:
+        listen:
+          port:
+            $secret:
+              file: secrets/port.txt
+    `,
+    '/secret-port/secrets/port.txt': '12345',
   };
 
   return {
diff --git a/packages/config/src/reader.test.ts b/packages/config/src/reader.test.ts
index 41cdc92938..3fe74aa637 100644
--- a/packages/config/src/reader.test.ts
+++ b/packages/config/src/reader.test.ts
@@ -88,7 +88,7 @@ function expectInvalidValues(config: ConfigReader) {
     "Invalid type in config for key 'string' in 'ctx', got string, wanted boolean",
   );
   expect(() => config.getNumber('string')).toThrow(
-    "Invalid type in config for key 'string' in 'ctx', got string, wanted number",
+    "Unable to convert config value for key 'string' in 'ctx' to a number",
   );
   expect(() => config.getString('one')).toThrow(
     "Invalid type in config for key 'one' in 'ctx', got number, wanted string",
@@ -580,4 +580,17 @@ describe('ConfigReader.get()', () => {
       },
     });
   });
+
+  it('coerces number strings to numbers', () => {
+    const config = ConfigReader.fromConfigs([
+      {
+        data: {
+          port: '123',
+        },
+        context: '1',
+      },
+    ]);
+
+    expect(config.getNumber('port')).toEqual(123);
+  });
 });
diff --git a/packages/config/src/reader.ts b/packages/config/src/reader.ts
index 65143bbd95..eb8c91e366 100644
--- a/packages/config/src/reader.ts
+++ b/packages/config/src/reader.ts
@@ -49,6 +49,9 @@ const errors = {
   missing(key: string) {
     return `Missing required config value at '${key}'`;
   },
+  convert(key: string, context: string, expected: string) {
+    return `Unable to convert config value for key '${key}' in '${context}' to a ${expected}`;
+  },
 };
 
 export class ConfigReader implements Config {
@@ -183,10 +186,22 @@ export class ConfigReader implements Config {
   }
 
   getOptionalNumber(key: string): number | undefined {
-    return this.readConfigValue(
+    const value = this.readConfigValue<string | number>(
       key,
-      value => typeof value === 'number' || { expected: 'number' },
+      val =>
+        typeof val === 'number' ||
+        typeof val === 'string' || { expected: 'number' },
     );
+    if (typeof value === 'number' || value === undefined) {
+      return value;
+    }
+    const number = Number(value);
+    if (!Number.isFinite(number)) {
+      throw new Error(
+        errors.convert(this.fullKey(key), this.context, 'number'),
+      );
+    }
+    return number;
   }
 
   getBoolean(key: string): boolean {