diff --git a/etchosts/etchosts.go b/etchosts/etchosts.go
index 256a89dfa8..5f68372b90 100644
--- a/etchosts/etchosts.go
+++ b/etchosts/etchosts.go
@@ -182,6 +182,6 @@ func Update(path, IP, hostname string) error {
 	if err != nil {
 		return err
 	}
-	var re = regexp.MustCompile(fmt.Sprintf("(\\S*)(\\t%s)", regexp.QuoteMeta(hostname)))
-	return ioutil.WriteFile(path, re.ReplaceAll(old, []byte(IP+"$2")), 0644)
+	var re = regexp.MustCompile(fmt.Sprintf("(\\S*)(\\t%s)(\\s|\\.)", regexp.QuoteMeta(hostname)))
+	return ioutil.WriteFile(path, re.ReplaceAll(old, []byte(IP+"$2"+"$3")), 0644)
 }
diff --git a/etchosts/etchosts_test.go b/etchosts/etchosts_test.go
index a79b43b6b7..13e3a211d6 100644
--- a/etchosts/etchosts_test.go
+++ b/etchosts/etchosts_test.go
@@ -137,6 +137,55 @@ func TestUpdate(t *testing.T) {
 	}
 }
 
+// Regression test for GitHub issue #603
+func TestUpdateIgnoresPrefixedHostname(t *testing.T) {
+	file, err := ioutil.TempFile("", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(file.Name())
+
+	if err := Build(file.Name(), "10.11.12.13", "testhostname", "testdomainname", []Record{
+		Record{
+			Hosts: "prefix",
+			IP:    "2.2.2.2",
+		},
+		Record{
+			Hosts: "prefixAndMore",
+			IP:    "3.3.3.3",
+		},
+		Record{
+			Hosts: "unaffectedHost",
+			IP:    "4.4.4.4",
+		},
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	content, err := ioutil.ReadFile(file.Name())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if expected := "2.2.2.2\tprefix\n3.3.3.3\tprefixAndMore\n4.4.4.4\tunaffectedHost\n"; !bytes.Contains(content, []byte(expected)) {
+		t.Fatalf("Expected to find '%s' got '%s'", expected, content)
+	}
+
+	if err := Update(file.Name(), "5.5.5.5", "prefix"); err != nil {
+		t.Fatal(err)
+	}
+
+	content, err = ioutil.ReadFile(file.Name())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if expected := "5.5.5.5\tprefix\n3.3.3.3\tprefixAndMore\n4.4.4.4\tunaffectedHost\n"; !bytes.Contains(content, []byte(expected)) {
+		t.Fatalf("Expected to find '%s' got '%s'", expected, content)
+	}
+
+}
+
 func TestAddEmpty(t *testing.T) {
 	file, err := ioutil.TempFile("", "")
 	if err != nil {