diff --git a/src/utils.ts b/src/utils.ts
index ed0307a..d104a12 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -266,7 +266,7 @@ export const formatHost = (host: string): string => {
   if (host.startsWith(':')) {
     // if host starts with ':', prepend the default hostname
     host = `http://127.0.0.1${host}`
-    isExplicitProtocol = false
+    isExplicitProtocol = true
   }
 
   if (!isExplicitProtocol) {
diff --git a/test/index.spec.ts b/test/index.spec.ts
index d6756fd..3376ba3 100644
--- a/test/index.spec.ts
+++ b/test/index.spec.ts
@@ -13,6 +13,10 @@ describe('formatHost Function Tests', () => {
     expect(formatHost('1.2.3.4:56789')).toBe('http://1.2.3.4:56789')
   })
 
+  it('should parse with only a port', () => {
+    expect(formatHost(':56789')).toBe('http://127.0.0.1:56789')
+  })
+
   it('should parse HTTP URL', () => {
     expect(formatHost('http://1.2.3.4')).toBe('http://1.2.3.4:80')
   })
@@ -52,4 +56,8 @@ describe('formatHost Function Tests', () => {
   it('should handle trailing slash in domain with port', () => {
     expect(formatHost('example.com:56789/')).toBe('http://example.com:56789')
   })
+
+  it('should handle traling slash with only a port', () => {
+    expect(formatHost(':56789/')).toBe('http://127.0.0.1:56789')
+  })
 })