diff --git a/identity-server/src/IdentityServer/Extensions/StringsExtensions.cs b/identity-server/src/IdentityServer/Extensions/StringsExtensions.cs
index a92d2ff1b..c86503186 100644
--- a/identity-server/src/IdentityServer/Extensions/StringsExtensions.cs
+++ b/identity-server/src/IdentityServer/Extensions/StringsExtensions.cs
@@ -207,12 +207,9 @@ public static bool IsUri(this string input)
             return false;
         }
 
-        if (uri.IsFile && !input.StartsWith(Uri.UriSchemeFile + "://", StringComparison.OrdinalIgnoreCase))
-        {
-            return false;
-        }
-
-        return true;
+        return !uri.IsFile ||
+               // no need to check if input starts with {Uri.UriSchemeFile}:// because uri.IsFile ensures it is either '/' or `file://`
+               input.StartsWith(Uri.UriSchemeFile, StringComparison.OrdinalIgnoreCase);
     }
 
     [DebuggerStepThrough]
diff --git a/identity-server/test/IdentityServer.UnitTests/Extensions/StringExtensionsTests.cs b/identity-server/test/IdentityServer.UnitTests/Extensions/StringExtensionsTests.cs
index 364ca6615..2585626b5 100644
--- a/identity-server/test/IdentityServer.UnitTests/Extensions/StringExtensionsTests.cs
+++ b/identity-server/test/IdentityServer.UnitTests/Extensions/StringExtensionsTests.cs
@@ -176,7 +176,9 @@ public void IsUri_should_block_paths()
     {
         // especially on linux
         // https://github.com/DuendeSoftware/Support/issues/148
+        " /path".IsUri().Should().BeFalse();
         "/path".IsUri().Should().BeFalse();
+        " //".IsUri().Should().BeFalse();
         "//".IsUri().Should().BeFalse();
         "://".IsUri().Should().BeFalse();
         " ://".IsUri().Should().BeFalse();