diff --git a/pkg/format/pgre/pgre.go b/pkg/format/pgre/pgre.go
index 44334ee..78a20dc 100644
--- a/pkg/format/pgre/pgre.go
+++ b/pkg/format/pgre/pgre.go
@@ -5,6 +5,7 @@ import (
 	"context"
 	"fmt"
 	"net/url"
+	"strings"
 
 	"github.com/go-pg/pg/v10"
 	"github.com/vmkteam/pgdesigner/pkg/pgd"
@@ -50,7 +51,7 @@ func connectDB(dsn string) (*pg.DB, error) {
 
 // IsDSN returns true if the input looks like a PostgreSQL DSN.
 func IsDSN(s string) bool {
-	return len(s) > 11 && (s[:11] == "postgres://" || s[:13] == "postgresql://")
+	return strings.HasPrefix(s, "postgres://") || strings.HasPrefix(s, "postgresql://")
 }
 
 func parseDSN(dsn string) (*pg.Options, error) {
diff --git a/pkg/format/pgre/pgre_test.go b/pkg/format/pgre/pgre_test.go
index 4565ba3..dfd947a 100644
--- a/pkg/format/pgre/pgre_test.go
+++ b/pkg/format/pgre/pgre_test.go
@@ -81,6 +81,25 @@ func skipIfNoPG(t *testing.T) {
 	}
 }
 
+func TestIsDSN(t *testing.T) {
+	tests := []struct {
+		name string
+		in   string
+		want bool
+	}{
+		{name: "postgres scheme", in: "postgres://localhost/db", want: true},
+		{name: "postgresql scheme", in: "postgresql://localhost/db", want: true},
+		{name: "plain path", in: "docs/apisrv.xml", want: false},
+		{name: "trailing dot 12 chars", in: "docs/apisrv.", want: false},
+		{name: "empty", in: "", want: false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.want, IsDSN(tt.in))
+		})
+	}
+}
+
 func TestParseIndexColumns(t *testing.T) {
 	tests := []struct {
 		name string